Have I been sexually abused?

Okay, so recently I don't know why but I keep having these flashbacks of me when I was 4 years old (I'm 17 now) and I was taking a shower with my mother's boyfriend at the time. I just remember being inside the shower, seeing him naked and every time I happen to think about it I feel so uncomfortable and scared. But the fact is that I also remember my mom being there outside the shower telling me that everything was okay. I don't know if this is actually true or not though...

I also remember that, during the same period, so when I was 4/5 years old, I was pretending to have sex with a big doll I had and I was engaging in "sexual acts" with kids my age (like touching and letting them touch me and proper kissing...and I was 4). This kept going until I was around 10 years old.

And if I think about my mom's ex boyfriend, I can't remember anything good about him, not even one good moment we spent together. Just the really bad experiences. This one and that one time he slapped me so hard that I fell and hit my nose on the table and bleed. That's all I remember.

I also remember always feeling uncomfortable around him, all the time.

Please take this question seriously, this thing is really bothering me now...thanks.