What could a past (16 months ago) covid infection have done to me to where i am getting sick more frequently (every 4-6 weeks) when i used to only get sick once a year? all labs/tests/etc are normal?

This is not because you had covid. The same thing is going on for millions of people. Precautions against covid (masking, social distancing, etc) was effective in reducing the frequency not only of covid, but also influenza, common colds, and other viral infections. (There was little influenza last year.) That in turn left people more susceptible to these viruses as covid precautions were reduced.