It sounds like a superficial vein in the skin, not between the fascia. If so, it plays no role in erection and you could probably have it removed or ablated without consequence since the remaining veins would just adjust their size to compensate, but you might be able to get rid of it with more conservative treatment. You’d need to see a doctor about it.
It might not be a vein though.
If it is a vein, you may have a blood clot or infection in it.
Superficial vein thrombosis - Wikipedia
Since you’re in the USA, it’s very possible you might not have access to a doctor. If I was in your position, I would check my body temp to see if I had a fever, which could indicate infection. If there was no fever, I would rig a compression stocking around the penis, making sure it doesn’t cut off blood flow, and apply hemorrhoid cream. If there was a fever, I would put antibiotic cream on it immediately and try to find a low cost or free clinic. I’m not a doctor though, and this isn’t medical advice. I’m just writing what I would do.
Starting: 7"bplx5.2" 2017 (shrunk from disuse)(originally 8"bplx4.5", gained to 9"bplx6")
Current: 9.0"bplx6.125" 2020
Goal: 11.5"bplx7" 2021.