Talk to Gynecologist on Mastitis Or Clogged Duct

I’m 4.5 months postpartum and have been exclusively pumping without any issues. Since last night, I’ve had pain in my left breast and noticed a tender lump. I also haven’t been able to pump as regularly for the past 2 days.

Today the pain and lump are both noticeably better, but still quite painful but bearable but I’m confused about whether this could be a clogged duct or mastitis as this is the first time happening