Flat nipples - trying to breastfeed 😟

So I have flat nipples and I have nipple shields but I haven’t tried breastfeeding since Sunday (was trying to feed on the boob as much as I could) because it’s just too frustrating. The shield would fall onto his face and spills milk everywhere.

I mix formula and my breast milk to feed little guy but I want to switch to breastfeeding only.

I just did power pumping for 40 minutes, does anyone else have any other advice to increase milk supply or to help with feeding on the boob? Lactation cookies? Supplements I can take?

FTM - thank you in advance!