HI I'm 20, Male. I've Had Anal Yellowish Discharge For

HI
I'm 20, Male.
I've had anal yellowish discharge for the past 2 years. it is really uncomfortable and held me back from most of my activities. The discharge increases with exercise. Also it tends to come when the temperature is higher than when its colder.

I went to see a doctor like a year ago. And after examination he said it is not a fistula problem neither hemorrhoids.
I have never had any kind of sexual intercourse before so it is clearly not an STD.
The other thing is it seems to decrease to almost nothing sometimes and comes back on other times.
And now i'm really concerned. Any help would be appreciated.
Thanks in advance