Hello,
This crawling sensation can be due to overmasturbation causing nerve compression, prolonged sitting, allergic reaction, anxiety, contact dermatitis, diabetes, prostatitis, genital herpes or diabetes or vitamin B 12 deficiency.
Get your blood sugar and thyroid hormones levels evaluated. You can take some vit B12 for some days like Neurobion and see if the crawling sensation is gone or not.
If symptoms persist then get an evaluation done from a dermatologist.
I hope it helps. Take care and regards.