'll Start From The Beginning.. I Was With My Sex

'll start from the beginning.. I was with my sex partner for 4 years then we separated and have been seeing other people. But once in a while we'll still be with each other. (We have a 1 year old) now when ever I don't have sex with him I'll be OK nothing itches or burns or hurts I'll have sex with my bf and I'm fine won't feel anything. But when my ex comes around and we do it right away or maybe a lil while later I'll start to get very very itchy on my vagina it'll get so itchy it starts burning and it hurts really bad! I normally go to rite aide and get some monistat itch cream or anything for feminine itch. Up till now it has worked the itch and burn go away in like 2 days of using itch products. Won't feel a thing good as new until I have sex with my ex will it happen all over again. Only happens WITH HIM!? what dose that mean? Is it bad? Do I have an std? Should I be scared? Also... Recently i had sex with my ex we fell asleep but a while later I woke up cuz I felt bugs cwraling on my vaginal erea. Started using the itch products till today but the bug feeling won't go away and I'm scared.!? I haven't had sex with no one ever since I don't want anyone to get the bugs! :( I'm never comfortable any more and spend most time scratching and applying cream what dose this mean? What should I do!? Also when I apply monistat complete care instant itch relief Cream it burns really bad but after a bit it'll go away?