Supplemental Formula, Breastfeeding, & Weight Gain probs

Hello!!

I need some advice. My son is ten days old and my wish has been to exclusively breastfeed him. However, we had a delay in starting to breastfeed his first two days of life because the hospital was running tests and literally told me I couldn't breastfeed until they got the results. I still attempted to breastfeed him, but since they were telling me not to, I received no help until the end of the 2nd day when they got the tests back. I'm extremely upset about this because I feel like it's set us back but that's a whole 'nother conversation... so he went from 7 lbs 7 oz at birth to 6 lb 9 oz at 8 days. That's an 11% weight loss so his Dr. has us using Similac for supplementation at every feeding. so I breastfeed on each side for 10-15 minutes and then I give him the 2 oz bottle of formula. Trying to do this every 3-4 hours. I'm concerned about my milk supply...should I be pumping 2 oz every time I give him the bottle?? I really wanted to exclusively breastfeed, but now I'm just concerned about his weight and I just want him to get all of the nourishment that he needs. Please share your experience and any thoughts or advice that you have for me. Thank you!!!