I meant that your son is still very young and his digestive system is still maturing. Has he started dribbling lately? I think I said earlier that when mine teethed while she was still exclusively breastfed, the dribbling would often turn her poop green.
I know it's disconcerting to keep seeing green poops but it's genuinely not usually a problem as long as the baby is well and gaining.
Since it started after you began a probiotic, maybe that could be causing it. While it is lactose free, it will still be changing the balance/composition of his gut flora. Could you try not giving it, and use something like Infacol instead before a feed if gas is a problem? Has the probiotic helped his gas at all?
When we saw green poop, it usually lasted around a couple of weeks before it went away again on its own, but it did come back a few times. I don't think a bottle could be causing it, as he is still taking the same milk.
Had you been seeing yellow poop again prior to this green one? Maybe your pump isn't efficient enough to remove the hindmilk for him?
I don't really have any other advice or information. I'm sorry you are so worried about this! I do know how it feels. I remember WhatsApping my partner a jubilant photo of a yellow poop when we finally got one back. If you are still really concerned, I guess you could ask your doctor, but in my experience they just weigh the baby, say he/she is fine and then ask you if you have PND. Sorry if that sounds cynical - hopefully you have a better doctor than I do.
Don't suffer alone. If you have any more questions or concerns, I will try my best to help.