can you get pregnant from dried semen

You would not likely be fertile the day before your period started, and your period is a good sign that you are not pregnant.

Sperm cannot walk; they swim. They would have great difficulty getting through your underwear (unless very open-weave), and then would have to find their way into your vagina.

From what you have described, it is very unlikely you would get pregnant, even at a fertile time.

but i am experiencing headaches and nausea sometimes,and sometimes my mouth tastes weird.i searched it up on google and they said maybe its just me overthinking about it,and my body is tricking me into telling me im pregnant

I think you are probably 'overthinking'. But here are some more pointers to try to allay your fears:

1. "I had pre-ejaculation on my fingers, but I wiped it off on my clothes" Which is likely to have stranded any sperm; they need fluid to survive.
2. "he started to rub my vagina" - your actual vagina (birth canal) or vulva or what? For him to transfer sperm into your vagina there would have to be sperm on his fingers, but before then "he went to wash his hands with soap", so that is not likely.
3. "we had our underwear on", so unless anything went under your panties, any sperm would have to get through the fabric of your panties and into your vagina.
4. "I used the same hand ... to touch the area on my panties which was wet from my vagina." What sort of fabric? The fabric would need to be reasonably open-weave for sperm to get through. How wet? There would have to have been sufficient liquid to enable the sperm to swim. Was the 'area' wet or damp? Was the area you touched at your vagina entrance or did you just touch your clit?
5. Above all, you have had your period, and it was not likely a fertile time.

I hope this helps some more, but if you want to talk more, feel free (privately if necessary).