Need help for my 1 month old baby. Okay?

My 1 month old baby is on combination feeding from day 1 as my baby was born via c section. There wasnt milk supply until 3 days and then i had inverted nipples so it was very difficult to latch the baby. I started using nipple shield to breastfeed my baby and starting pumping and providing him milk and also started feeding similac plus from day 5. Today he is 1 month and 5 days old, im still expressmilk and giving similac plus but yesterday i saw some red strains in poop. Only 1 episode for now. The next poop was yellow but little slippery. I have less supply, so baby is fussy and still hungry after feeds so i am using lactare powder everyday 2 times a day . I am concerned about my baby and he makes weird sounds in the night and sometimes in the day. Feels like he is constipated or in pain but he does it when asleep. My question is," is formula feed okay?" Im feeling hopeless and so worried. I doing all things, eating dalia daily, pumping milk and also latching baby. Please advice