If you haven't seen an infectious disease specialist, it might be a good idea since you were in Mexico and there are myriad tropical bugs one can pick up.

My brother spent time in the Caribbean and, unbeknownst to him, picked up a semi-rare parasite. He had a lot of low-grade symptoms, and extreme fatigue, and saw multiple doctors when he got back to NYC. To no avail. Finally an infectious disease specialist diagnosed and treated the condition, thought to be caused by a bite from a waterborne insect that thrives in some lagoons near where he stayed.