I've had this odd feeling in my stomach since Thursday night, it's been like fluttery and felt like butterflies, I'm on the pill and when I finish a pack for a week I get my period, I don't have sex when I'm off the pill, I had sex a couple of weeks ago before came off it, my period started on last Sunday and finished this Wednesday, and had sex with my boyfriend last night although he has never came inside me, so I'm pretty sure it can't be pregnancy can it? What else could it be? I've also felt kind of nauseous but that's the usual for me, any ideas?

Take a appointment with a doctor .

Assuming you are taking your pills correctly, the time you are off the pills and are having your cycle is not be the best time for pregnancy.
But it will all depend on when you ovulate.

Also even if you have sex, when taking the pills, they are not 100 percent, and people get pregnant taking the pill all the time.

So could you be pregnant, yes but the chances are slim

You need a total checkup. You complained about nausea months ago, after eating home cooked food as opposed to your usual junk. Lots of cheap and fatty and fried foods, mostly meat and refined flours and the worst kind of fats and oils. I suspect that you are just plain unhealthy! Not knowing how long you've been on the pill, I'd say it's possible that the hormones might be making you queasy too. This sort of question is tough enough for a doctor to answer in person, and online is impossible.
Also, what to you drink? Are you getting enough fluids as it gets warmer (if you are north of the equator), and NOT soft drinks, either sugary or diet? AVOID those like the plague. I drink juices watered down about 10 to 1. Basically water with a tiny flavor to it.