Help I'm running out of milk

So I'm not sure what to do and I'm not sure if it really matters but I thought I'd ask you guys for help. I pump and breastfeed my daughter she's a month old but my milk has dried up all of a sudden yesterday I was pumping close to 3 oz every time and today I'm getting half an ounce I'm running out of breast-milk I have enough for two bottles left in the fridge. I have some formula I'd like to try. Until i get more breast milk in but for the time being we're going to have to use formula for her. I have a bunch of different brands I got as gifts at my baby shower and I got some samples sent to me. I just want to know what is the best formula to use for short time use until I can get my milk back up. Or what formula can I give to her after I breastfeed her to fill her up. Also will she get a tummy ache or anything switching up her milk all of a sudden

Also any tricks you guys know to help breast milk. I drink plenty of water and I started taking fenugreek I also eat oatmeal everyday.