Pregnant & trying to wean 15 month old

So, I am at 6 weeks and 4 days. I have a 15 month old who I have only been breastfeeding once or twice a day max. My body naturally decreased it's milk production at 13 months and no matter how much I try to breastfeed her it won't increase. This hasn't been an issue since she hasn't been demanding to be breastfed other than before sleeping and when waking and practically nothing comes out and she has started to hurt me because I'm guess my she is trying other methods of suction to get anything out. Now, the issue is that my daughter has had diarrhea for almost 2.5 weeks now. We have run tests for parasites, viruses, etc. and the pediatrician has seen her and nothing everything has come back negative. I noticed a coincidence with her diarrhea and my early pregnancy which I mentioned to him. I thought he was going back to tell me I was crazy but said there were no studies on it, but had heard about these cases/coincidences and that it could be probable that my hormones could be affecting her tummy. Anyway, after that long description - has anyone has a similar experience? And now, that I've decided to completely wean her to see if that alleviates her diarrhea, she has become a little demon crying and whining all day and all night - I know she feels rejected, so does anyone have any recommendations from going through something similar (we are back to sleepless nights with a screaming baby - she used to sleep fine throughout the night waking up maybe once and falling asleep on her own, but not anymore!)?