Hello I share your concern thus could be due to STI, allergic reaction or a manifestation of systemic disease like diabetes i see such patients in my clinic and i would advise you for urine culture and sensitivity test as well as culture of the discharge from the blisters You should be worried but not so much it may be due to friction or wearing tight undergarments so if you can update me about your weight and working culture I will be able to guide you better meanwhile maintain good hygiene by washing it with antiseptic solutions change the undergarments and wash and dry it regularly and properly HAVE PLENTY OF FLUIDS hope this helps you regards.