I've been freezing more milk than we use, and the oldest is now about 3.5 months old. Everything that I read has a different opinion on when it expires, but many sources say 3-4 months in the type of freezer that we have (attached to the fridge but with a separate door), but now I'm wondering.

We used some of it to mix with DS's (6 months old) oatmeal, and about 3 hours later he started vomiting violently. It continued until his stomach was completely empty, and then he was still wretching every time I tried to put him down. I had to hold him upright and rock him for a few hours before he could sleep horizontally. He woke up fine the next day though.

Now I'm wondering if it could have been the milk that caused the vomiting. We just started him on solids recently, but he'd had the oatmeal 3-4 times before this. It's a one ingredient cereal (not mixed grains).

Do I need to throw out the oldest milk? If so, what's the cut-off point? I hate to do that without knowing that it was the milk. Even if it was, it's possible that it was just that one bag, right? Is there a way for me to tell if it's bad before giving it to him?