Baby doesn't like to eat anymore? (Long)

krissi813

DS was EBF until he was 11 weeks old. He had had bottles of BM here and there but at around 11 weeks, we had to get him to eat mostly from the bottle because I was going back to work. This was a serious struggle because he hated it at first. I ended up EPing for about two weeks and we added some formula because I didn't pump as much as I should have. In fact, I hated pumping and figured that pumping and bottle feeding was just too much work for me and tried to gradually reduce my supply. After my first week of work, I realized how much I missed breastfeeding and started putting baby back to breast on nights and weekends. Now he is easily able to go back and forth between bottle and breast but sometimes does get frustrated at the breast. 

In any case, bottle or breast, LO does not seem to like to eat anymore. Sometimes he takes 4 oz bottles no problems, but most of the time, he only takes between 2-3 ounces every 3-4 hours during the day. When we are home, he does want to nurse every 2 hours or so (even at night, he only goes 3 hours) but he doesn't eat for very long and gets frustrated after a while. LO is definitely teething and I know this is affecting him, but I know he should be eating more.

LOs weight gain had definitely slowed and he is small for his age (maybe a little over 13 pounds at 14 weeks - he was 8lb 4 oz at birth). His 4 month appt is not for another 2 weeks and I am so nervous for him to be weighed. 

What is going on?