I'm thinking of selling my period stained underwear
Why would you sell your stained underwear?
Because it makes me feel like a dirty whore.
Wanting to sell your old underwear to feel bad about yourself is degrading and self-destructive. Raise your head up and take heart in the fact that you are a good person.
How about if I donate it instead? Is it okay to feel like a dirty whore for charity?
I don't think it's a money issue, it's about having respect for yourself. I'd prefer that you do things that make you feel like a smart and caring person than things that make you feel like a dirty whore.