Kitten all of a sudden acting strange?

I rescued a kitten. He is about 6 weeks old and litter trained. All of a sudden he peed on my bed while I was sleeping in it. So I took my sheets and washed them. I was home all day yesterday and used the litter box just fine without me helpin him and he was on my bed yesterday. I woke up today and he peed on my bed when I was sleeping again. Someone said he could be marking his territory but vet said he was too young and it is only when I am sleeping and he sleeps with me. I have clothes sitting on my floor but those are completely untouched. I have had cats all my life and never had one do this, all the other ones would have went for the clothes on the floor. If the only solution is getting him fixed he is way too young. Is there anything I can do?