Clumpy vaginal discharge

Question: I've been having this white clumpy discharge that looks like wet toilet paper or cottage cheese (sorry for the comparison) then I had my period and I thought it would go away but my period ended and this discharge came back. Now whenever I have sex it hurts to the point where I have to stop. My boyfriend has been very comprehensive and even worried about it. I am on birth control pills and also centrum for women but I don't think that's the issue because I've been taking these pills or a while and nothing has happened before.  What do you think it is?? Is it serious??