Is a red blister inside my cheek a blood blister or cancer?

Not necessarily . You need to have your doctor look at it.
Blood blister. If it hasn't been there for more than a few weeks and it's in an area where you can accidentally bite your cheek, it's a blood blister. Keep an eye on it. If it doesn't go away after a few weeks, see a doctor or dentist.

Related Questions

I have two small dark red blood blisters on my right inner cheeks. I never had them before and I don't remember biting my cheek either. They are not painful at all. Help.

See a dentist. If the blood blisters resolve in a 2 week period. Most likely you will be fine. If they persist, then have your dentist look at them. You probably got them from biting or from eating sharp/hard foods. Read more...
See a dentist. They are probably heamtoma's related to cheek biting. If you don't remember, you could have done it in your sleep. You should have it checked by a dentist to be sure. Read more...
Likely local trauma. It is most likely local trauma from the teeth but should be examined by a doctor to ensure nothing else is going on. There are viral illnesses and other local infections/masses that can present this way and a good exam will hopefully exclude anything serious. Read more...

Something that looks like a small blood blister appeared under my eye a few months ago and is still there. Could it be cancer?

It can be if it grow. Any pigmented lesions on the skin are suspect for Cancer when they are new, if they are growing in size or changing in their color, shape and size.If you want to take good care of yourself, you should show it to your dermatologist or to your family doctor soon. Read more...
Eyelid Lesion. Would need to have it evaluated by an Ophthalmologist or Dermatologist to know for sure. Read more...

I have a mole on my back that has started bleeding on its own, it's now formed what looks like a blood blister over it, could it be cancer?

Go to see derm. You should go to see a dermaologist and have that mole removed. Bleeding on the mole by itself would be one of the symptoms of cancerous mole. Make an appointment as soon as possible and have that mole checked and removed. Don't delay. Good luck. Read more...