I agree with Judy on this as well.
I would normally say, it's from the intercourse or possible infection, but after reading your health profile I recommend that you make a quick phone call to your gyne and express your concerns. It could be anything from side effects from the strong medication you are taking for your illness or it might be something that needs to be looked at closely. Only your physician is the person qualified to evaluate, diagnose and treat you, because of your past history. Don't wait, call an you will be informed if it will be necessary to come in for a check up. Good Luck,Judy