Hi there greg.
From your clinical description, it does not seem to be an STD & you say you have checked but why would you consider this theory?
Dermatology is a visual field
& it is best if you were to upload an image of the lesions or go across to a dermatologist
nearest you for a second opinion
& perhaps do a skin biopsy
Eczema is of different types & what your sister has may be a different variety.
What you have is probably pompholyx
which is a type of eczema & is multifactorial.
However, do get yourself checked for Herpes 1 & 2 IgG & IgM.
Use of a topical fluorinated steroid may help resolve symptoms.
Dr Praveen Rodrigues MD