Does a painful bump on the roof of my mouth indicate a sinus infection?

Unlikely: Bump on the roof of your mouth, your hard palate, can be lots of things, depending on associated symptoms. If it is painful blister - probably viral infection. If non-painful growing lesion or last > a week - need to see ent. Your right and left maxillary sinuses are located above your lateral palate and under your cheeks, so you can have palate or teeth pain if you have a sinus infection.