I don't know if my dad raped me?

When I was 8 I started getting abnormal sexual feelings that I couldn't explain. My little sister (who I hardly see becoz my dad had kids with too many girls) she once touched me and said "doesn't that feel good?" She was 6 at the time and I was 10... I thought that was very abnormal and I pushed he hand away and got a really sick feeling. When I was 12 I started getting panic attacks and I was diagnosed with depression (I take medication for both now). I'm now 14 and I'm starting to have flash backs of my dad raping me, I never see him anymore but it's really disturbing me....and now that I started getting flash backs I realized that if my memory is true that my sister might have also got raped by him because she touched me when she was only 6 years old. My flash backs are happening more often and I'm frightened about this. Help?