Had strep. Finished meds (z pack/prednisone). Week later, sore throat again + bad headache (I have migraines). OTC no relief. Urgent care or wait? Thx

Urgent care. Why wait and suffer with the headache? Also check to see if the Z-pak took care of the strep as sometimes you may need a re treatment or different antibiotics.
Viral infection. Concomittent viral infections in throat, on top of strep are quite common and may have been exacerbated by steroids you took earlier. I would give sometime before another trip to Urent care center for another round of meds, that may not be indicated. Just use ibuprofen or chloroseptic spray/lozenges for symptomatic relief, along with plenty of vit C and fluids.

Related Questions

What to do if I have strep, sore throat w/ white spots/swollen gland. Can I take a z pack (azithromycin) with my daily meds?

Strep throat. Strep throat should be diagnosed by rapid strep test and/or throat culture. Azithro is acceptable alternative if allergic to penicillins. Short course of Azithro is generally fine when taken with other medications, however, there may be some specific drug interactions. You should check with pharmacist if you have specific concerns.