IF you are using a condom put some lube inside the condom tip. This will bring more pleasure to you. If that is not the case think of the most sexual act you can think of or put some porn on. Don't masturbate for a couple days before sex.
This is very common. Ask the guys who ride bikes on the trail and they will say they have the same problem. The problem is the seat - the bike seat - is too small and it just kinda goes right up the area you described cutting off blood. You will actually damage that are if you continue...
You could be so concerned about the pain that you are not getting sexually aroused enough to cause enough natural lubrication. Try some lube that you can buy at Wal Mart. It could be that your bf is too rough and pounding you like there is no tomorrow. If that is the case just ask him to slow...