Need help increasing my supply!

I’m 4 months postpartum, I only pump about 21 ounces a day. My daughter was born at 4 pounds, she would drink about 18 ounces for a while but she is now 10 pounds & is starting to drink more than what I can pump her. I’ve tried pump princess pills with my prenatal, honestly haven’t seen a difference. I pump 7 to 8 times a day only getting 3 to 2 ounces a pump. I use the spectra pump, I only get about one good letdown on it. It usually is right when I start pumping on simulation mode. I change the mode to different expression cycles & I get nothing but maybe lil droplets. I was using the Medela freestyle pump for a while too but I still have the same output as with the spectra. I have no idea how to power pump on my spectra I definitely want to try that. I would power pump with my medela. I’ve been dipping in my freezer stash & i only have one full bag left. I’ll have to start combo feeding if I don’t up my supply. I want to strictly give my baby breastmilk. Any tips would help! I’m desperate, I feel overwhelmed not producing enough.