For The Past Couple Days The Edges Of My Ass

For the past couple days the edges of my ass crack where the cheeks rub have started to hurt/ get inflamed from chafing i believe. It's been hot out and i've been wearing some loose fitting underwear latetly so i believe that is the cause but i figure i would check it out. It usually doesn't start hurting till my 10 or 11th hour working.