I am a college student with no sexual activity. about 5 nights ago a girl gave me a blowjob and that was it. ive masturbated 3 times since that night and everything was fine until just this last night where my cum was a brown color. do you know why?

How brown? A slight brown tint is not a cause for concern. In any case neither the blow job nor your masturbation is a likely cause. Get HPV vaccine. Use a condom all the time you have any sexual contact, including a blow job. Wish you good health!

what you describe IS sexual activity. Congestion of the prostate or prostatitis , both can give you brownish ejaculate which should gradually clear up. If it does not or gets worse see a Urologist. Of course use precautions when having sex