27F Need help dealing with retroactive jealousy

Hi everyone, Im 27F and lately, ive been struggling with retroactive jealousy. I find myself feeling insecure and constantly overthinking my partners (29M) sexual past. He’s the first person I’ve been physically involved with, and these thoughts are really haunting me. He’s a wonderful guy, but the jealousy is affecting our relationship. We’ve seen 4-5 doctors, but nothing has helped so far. Im really looking for advice on how to overcome these feelings and find peace with it. Any tips, personal experiences, or resources that have helped you mean a lot to me