bluey2223 saidWhen I was a teen I had thick and volumous stuff... In fact, I don't even have to clean up after I make love to myself.
A change like that at 25 is worth a trip to the doctor, for a possible referral to a urologist. You likely will get your prostate checked with a DRE (digital rectal exam) as a minimum.
If also requested, providing a semen sample for lab work can sometimes be done at home, into a small capped cup they provide, but you typically have to be able to return it to the office or lab within about 15 minutes or the sample is worthless. Alternately, they may require you to masturbate on site.
Which can be kinda awkward & embarrassing, even alone in a small closed exam room, since you know the staff is aware of what you're doing inside, and waiting for you to get it done. I've given semen samples both ways, and in the office setting they had Playboy magazines laid out in the room as an aid. If that's unlikely to help you, and I doubt many offices even today will have Colt magazines or the like as an alternative, it might be a good idea to bring some gay porn images of your own folded in your pocket, or on your smart phone.
In any case, I would encourage you to have this checked soon. You may have some infection or other problem with your prostate, or elsewhere in your reproductive tract, which can be serious if not treated.