Supply down after sick baby

An

So my little one is recovering from a bad case of pneumonia (not bad enough where she had to be hospitalized thank goodness) but bad enough where she didn't want to nurse normally for a few days. I pumped when I could (maybe about 4-5 times in total those 3 days) but now shes back to nursing semi normally and I'm noticing my supply has gone down. My breasts feel flat and empty, less let downs and when she unlatched, I squeezed my boob a little to see if there was any milk and nothing. Any advice on how to boost it again?? She won't take bottles so that's a big concern for me if we would have to end up changing to formula.