If bub is otherwise happy (ie. alert, looking well hydrated and wanting to feed as usual) I'd also be going with too much foremilk. Frothy or not, green poo is usually a result of that. Are you feeding from both breasts at each feed or letting him completely drain one and then offering the next one next time?

Bear in mind if you go to the doctor in the morning - most doctors are completely oblivious to variations in bowel movements in a breastfed baby - they learn nothing about breastfeeding in their training (even paediatricians only cover the basics which is scandalous really). If your baby is ticking all the boxes above, it's not diarrhoea. It is very, very unusual for a breastfed baby to get a stomach bug, particularly if no one else in the house is affected.

Keep feeding. Even if it is diarrhoea, which I doubt, breastmilk is the best thing for him and at 10 weeks, all he needs.