There are a few guys (although not all) that I've had sex with and have felt like I was in love with them after it. I had no such feelings before and here's the problem... these 'feelings' go away after a few days. Im so confused, any advice?

That's how the female brain works. As we experience the physical closeness of cuddling and touching and kissing and other intimacies, it's our emotions that tell us (in order to make it okay that our usually well-guarded defenses have been breached), "This is okay and this is good because he cares about me and maybe even loves me." And once the ultimate act of love has been shared, our brains go into overdrive that this certainly must be love for both of us. Too often, we find out sooner or later there there was no real love there at all and are then thrown into a tizzy of emotions that might include regret, anger, guilt, depression.

That's why it is so important that the love be there first before the consummation of it in the very physical and most intimate act of sexual intercourse.

Stop having sex till you are with them for several months at least and feel in love with them first.

It is better to have the connection before sex, but you never said you were necessarily looking for a relationship or any kind of commitment.
Sex is a very emotional act even if the person you are having sex with and you do not have a strong bond. Even the act of sex releases certain hormones that can kind of put you in that love phase. More than likely it might be a psychological thing though too like wondergirl said.
It is good you are acknowledging the feeling as false though. Don't let yourself get caught up in a false love/ emotions; it is probably only going to lead to you getting hurt.

Love/Lust/Attraction are intense feelings and some times its hard to tell the difference when you are feeling them.Thats why its important to know how you feel before adding sex to the mix.

We are attracted to many others, but love grows, lust fades. If its return the way it was given. Hurts when its NOT. So imagine the pain of two people who think they are in love, yet there is nothing after the lust fades.

That's why any confused hearts hurt so bad.