my boyfriend and i had sex at 2am and then when we woke up at 12pm the next day, before giving him head, i started to rub/stroke his penis like i normally do to wet the penis. normally there'd be clear fluid at the head of the penis. however, this time i noticed there were LOTS of little yellow particles within the clear fluid (they looked 'mushy', not stone hard). We have never seen this before. Should I be concerned? What are they? STDs? Infection? Prostate problem? I considered perhaps remnants of whatever made it out in the ejaculatory fluid from 10 hours ago, but we've had sex in that kind of short time frame before and never have I seen this yellow stuff.

of course, when I asked him what it was (in a light-hearted jokingly manner), being a man, he didn't say anything (probably too embarrassed).

Btw, we're both young. in our early 20s. Been dating each other for several years now. thank you in advance.