What does it feel like if your tooth has a cavity? I've never had one, but I have a spot in between two teeth that hurts. I'm not sure how high of a priority getting to the dentist should be.
Sadly my flossing habit went out the window for the first 5 months of M's life, so I wouldn't be shocked if something bad happened.
What kind of pain are you having? Cavities are usually pretty advanced before they start hurting (much older than 5 months). But usually people experience cold, sweets, and/or pressure sensitivity when they have cavity related pain.
Any chance that you clench or grind your teeth? I go through phases where I clench my teeth so badly that I will have pain off and on. If you're having pain I would put a visit to the dentist at the top of your priority list, because tooth pain can flare up really quickly and it SUCKS.