How can you tell if pain is caused by tooth decay, sensitive teeth and sinus pain?

See your dentist: Decay will usually be sensitive to cold, possibly hot, and maybe sweets. Sensitive teeth as in excessive grinding will usually be sentitive to cold and sometimes pressure. Sinus pain is usually in your upper back teeth and usually tender to pressure. Bend over and touch your toes, if your head feels like it is going to explode then it's your sinus, plus probably congestion also.

See a dentist: Dental pain could mean many different things. Among them, as you point out, are tooth decay, sensitive teeth, or sinus problems. You should see a dentist who can tell you whether or not the problem is dental. If you have no obvious dental issues, you may then see an ENT specialist who can tell you whether or not your problem is sinus-related.

Pain : My first answer is get an exam and x-rays to determine if there is decay present causing the pain. Sinus pain will generally increase if you bend over while standing to pick something up off the floor.