Well before we have sex my boyfriend fingers me and then we will have sex and its fine at first but then in the middle of it its starts to burn and hurt and I don't know why what could it be?

Have you tried lubrication?

Yes

You think you're pregnant. Are you subconsciously "clamping down," a nervous reaction.

Marie, do you normally use birth control? If so, what type?

It could be a reaction to the lubricant you are using. If you are using condoms, it could be a reaction to the materials used in them.

It could be friction. As Judy said, you could be clamping down from concern. It could also be muscles contracting as you get close to orgasm.

If it is happening 'half-way' through, it may be that you are losing arousal and lubrication. If you are doing the same things each time, you might try doing things differently like changing positions.

What do you mean clamping down?? And no I'm not on birth control but it even does that without condoms and I'm not sure but I think I could be pregnant but going to find out at the doctors.

"clamping down" tightening your muscles making it hard to him because of mental worry.
And of course possible infections since some of them can cause pain in intercourse

I don't know I will have to find out