How do I get my BreastMilk production to increase??? 😕

I started off breastfeeding for about a month when I had my baby. Then, I started supplementing with Infamil because the Doctor's told me that my baby wasn't picking up the weight they were looking for...they recommended that I supplement with Infamil. Then, I completely stopped breastfeeding...because formula feeding was easier. I still have milk and I want to begin breastfeeding again...but my baby is rejecting my nipple. I tried pumping but it's not enough to feed my baby. So, she is still exclusively on formula although I have tried feeding her my milk and she fed for a few minutes then she rejected. She is now two and a half months old. Does anyone have any suggestions on how to increase my milk supply??? Even if I have to pump...I'd rather give my baby my milk instead.