I recently took my toe nail polish off after a couple weeks and found one of my big toes had a black spot. Is it a fungus or a bruise?

Most likely bruise. Nail trauma is common, whether from repetitive impact from running or just bumping into something . Fungal infections of the nail tend to be associated with yellowish, thickened nails. A dark spot on your nail that doesn't improve over a few weeks should be examined by a doctor to rule out the fairly rare nailbed melanoma.

Related Questions

Is the black spot on my toe a bruise or toenail fungus? How to tell?

See the podiatrist. A bruise is the result of a blood blister under the nail plate which can lift the nail plate from the underlying bed. This could lead to toenail fungus. However, not all black spots are bruises or infections, like fungus. There is other growths that discolor the nails, including some cancers. To be safe, have a podiatrist examine your toenail. Read more...
Third possibility? In this case, the best thing to do is to take a biopsy. The thing i would be concerned most with, and this is a very small chance, is some sort of skin cancer (melanoma). This is very important that you check this one out. Read more...

Discovered one white spot with some black flecks under my big toe nail. I don't know how long it has been there, as I've had nail polish for months.

Discovered one white. White discoloration usually comes from fungal infection , black could be from fungal infection/dry blood/very rarely skin cancer. It is best to see a podiatrist to get examined, possibly cut back the toenail and get sample of the nail for culture and possibly biopsy of the skin under the toenail, if needed. Read more...