Pain after?

I've been having pain after sex. It feels like everything is completely tigy and cramped up and the walls of my vagina throb terribly. I've had the same parter for the past year and I know that we are both clean of STDs. If we try to have sex again afterwards it burns terribly when anything is inserted into my vagina. We use plenty of lube so I don't understand what the problem is. Has anyone else ever had this issue?