parasites can live in dirt and sand and can be found in dust bunnies in your house if you have animals or if an airborne egg happens to land in your house. You can inhale airborne eggs from parasites and they can enter through your skin while walking barefoot. You can get them from unwashed fruits and veggies, or undercooked or raw meats. You can get them from contaminated water, even while swimming. We live in a world filled with parasites. They are opportunistic and work hard to hide and multiply.
So it's entirely possible that you have picked up parasites without traveling out of the country. It is possible that you picked up parasites from your turtle. Most animals in the wild have parasites. For a good read on that subject, read parasite Rex by Carl Zimmer.
You seem convinced that you have worms. Start a parasite protocol for worms. There are several on this forum. Some people have been successful with drugs, others with herbs.
I would recommend that you search this forum and read some of the success stories. Some people have eliminated small parasites with apple cider vinegar while others have used strong drugs sourced from farm supply stores.
As a general rule, parasites are really hard to identify as a specific type. Many people digest most of the parasite before expelling it. It sounds as though you may have roundworms but I have never heard of them being black. Most worms are flesh colored But if you got them from your turtle, anything is possible.
Good luck and come back if you need more help.

The picture is not of sufficient quality to be of value. Unless you have seen these gnats flying off your head I would not believe they are gnats. They are probably hook worm. Dead hook worm are black and they appear black when coming out of the skin. They are even in rice.

They are everywhere and most people have them and don't know it. You could kill them on your head but they are through out your system now. You will need to use meds like fenbendazole. This simple parasite seems to be the hardest one to eradicate. I don't want to offend the Alt Med people but you should go to the parasites RX forum and just start reading everything. Make the assumption they are hook worms because you won't find a thing on gnats.

Gnats do not infect the body as they are flies. They lay eggs on food sources to feed their larvae. They need air to develop. If you are seeing gnats flying make sure they are actually there and not in your eye swimming by your cornea. (It happened to me.)
I also had hook worm in my scalp and was constantly feeling little bumps.

In the interim try a head lice treatment for the scalp problem. The drug should work partially for gnats or hook worm. Temporary relief until you can do the appropriate drug research to solve your problem.