Virginity and depression? I guess?

I'm 17 and about a week ago I had sex with my boyfriend for the first time w protection. I got super uneasy and I was expecting to be more happy as it was my first time and all. Fast forward to yesterday, I had sex with him again and once again my mood went down. I feel, to put it in more simpler terms, sad. I mean I'm always happy to be with him it's just when we get down and dirty, I tend to feel unhappy.