My breast milk is starting to smell?

Catherine
So my son is 13 weeks old and I breast feed and give him pumped bottles as well. But yesterday I heated him a bottle from the fridge and it smelled horrible. It was super strong once it was warm. It smelled like a burned chemical/plastic. I thought something must have happened and dumped it. So I heated him up another bottle ( smelled fine when it was cold) and that one smelled when it was warm to but not as strong! I've been trying to figure out what changed or if it was the bottles but my empty bottles smell fine... my breast pump parts have the same weird smell to them though even when clean. And the fresh milk I just pumped smells like it to? Any idea what's going on? I don't remember it smelling ever before. I've been doing the whole 30 diet so I've been eating healthy...