I Have Had A Feminine Issue For The Passed 2

I have had a feminine issue for the passed 2 months. Me and my ex-boyfriend decide to try to make things work. While we love each other very much and our relationship has never been better ( we were together for a little over a year and split up for several months) and now we are determind to not give up on each other over petty small stuff like the last tme. But I digress. The issue that I am having is that after we have sexual intercourse (we do not use condoms, just my nexplanon birth control implant so I don't end up pregnant), we like to lay next to each other (and I'm sorry if this is to graphic) until he goes soft inside me. Some times we even fall asleep life that. But I have been having a weird yellowish white discharge with an odd smell about a day or two after we have done this. It only takes about three days to go away, but I'm wondering what this could be from. I read on a medical website that it could be that our ph balances are different, with his being higher than mine and causing this problem. I would extremely appreciate your help as soon as possible that way I can figure out what is going on.