First of all, let me explain that my husband does not have a consistent schedule, he works close to our home but at times, due to his field of work, is sent out to do work that can last days, weeks, or even months at a time and they come up last minute without much warning. A lot of times we don't know how long a job will actually last and when he'll be home, which doesn't help the situation! And I also want to mention that I am a stay at home mom so my son and I are together ALL the time!

Okay, now on to my 2.5yr old son, he recently has been showing signs of depression, he has had some separation anxiety in the past, but that seems to only happen during the first few days my husband returns from a trip, and it does not happen every time he returns. This is the first time I've noticed him being severely irritable, weeping and whining frequently, he will throw a temper tantrum and cry over things that are "silly" that he never used to, like if I pick up or move something, is one example. He refuses to talk to his father on the phone and will smack my hand if I hold the phone out to him. He will start crying and fight me when I am trying to do things with him, like trying to get him dressed, bathed, hygiene things especially when brushing his teeth and using the potty. I ask him what's wrong and he tells me he misses Daddy, I tell him I know I miss him too, and that Dad misses us but has to work. And I don't know what else to do or say to help him. He seems to be sleeping less during the night and taking longer naps during the day, and is very sluggish about getting out of bed. He also seems to not want to leave the house without putting up a fight, unless we are going to see his Grandparents. He is normally a super energized kid and lately he doesn't seem to have his normal energy level and if I try to make an effort to play with him he seems to lose interest quickly in what he's doing or gets upset easily and runs off crying. I am at a loss for what to do, I am 8mos pregnant and can't take the physical stress of fighting with him every day because he makes it almost impossible to carry him when he's kicking and screaming! Anyone have any advice?

Sounds like a typical two year old to me.
That's why they call it the terrible twos.

It does sound almost normal for a child your son's age to be showing these unpredictable emotions.

I also think that it might be possible that he is acting irritable because he misses his father,my daughter used to act a bit more restless when her dad goes away for a few days.But that could be because he is always around and when he is not there,she misses him.

Another reason might be that he is not getting enough sleep and this in turn will make him tired the whole day, which in turn maybe preventing him from enjoying his usual activities.

If you could take him for a swim or an activity which will help him take out the stress and feel tired enough for a good night's sleep.

Thanks for the advice, however I am certain this is not just a typical toddler going through terrible two's, my son has his moments which I am well aware of, and if it were only that I would not be concerned! His grandparents and father both agree this is not just his terrible two's phase! This is extremely unusual behavior for him! I do try to take him to the pool, to the playground, and other activities but they always end up in a huge fight just to get him out the door because he is not interested in leaving the house, I have to pretty much drag him out the door because he is not interested in doing anything but watching T.V. Seems to be defeating the purpose of trying to get him out of the house to get his mind off things when I seem to be upsetting him even more (and also frustrating myself)! The T.V. seems to be the only thing that makes him somewhat happy! And to clarify my son has never really be affected much more than a little moodiness the first day or two his father goes on a trip and returns to his normal self after that, so I am not expecting him to not be affected by his father being gone, he is a daddies boy so I expect some sort of sadness, this is just totally off the wall extreme for him. But his dad's trips are normally more spaced out, however this time he had previously gone on a 2 week trip, my son didn't seem to be phased much by it, hubby came home and all was well but he had to leave after only being home for 1 week and my son has just now started with all these extreme emotional changes!

Basically he needs to learn to adjust.
When toddlers see you are revolving around making them comfortable learn to use it against you.
You need to keep reassuring him that daddy loves him and everything is fine. But obviously he needs to learn to adjust to your situation.
Your husband can't just quit his job to fix any problems. I think time and working with him to get him to adjust and comforting him is the only real solution at least at his age now.
You can take him to a dr or even a psychologist if you feel it is that bad.