I'm 19 I Had Been Masterbating 3 Times A Day

I'm 19 I had been masterbating 3 times a day until I noticed my sperm became yellow and thin. I refrained from masterbating for 2 days and tried again, when I came it was normal and milky but when the last shot went off it was thin and yellow with very small white things in it. I'm very frightened of what I may have. Also i am a virgin so it can't be an std