Welcome to HCM.
Unprotected oral sex
has very low risk for HIV
transmission as per CDC, Atlanta.
Loosing beard hair is nothing to do with either any STD
TestS for STD s will be more reliable after 4- 6 weeks. P24 Antigen test after 14 days will be reliable but more conclusive after 3-4 weeks.
Your sister's problem could not be related to yourS, unless there is sex between you and her. Familial hair loss may be appear for both. Consult your physician, he/she will guide for further investigations and find out the cause for your hair loss and treat you better.
Get well soon.