I get blisters filled with blood around my menstralcycle,,

I have noticed that I have had to cycles and both times I have gotten a patch of blisters I went to the doctor and was test for herpes and all other stds but it has come back negative I am not sure what it is they are not really painful but I can feel them and I know they are there if would have to say a. Feeling I would say itchy at best but not really. Anyway I don't know what to believe I know I don't like seeing any foreign things going on with my body they evebtook a piece of it the one of the blisters and said it wasn't herpes. By chance do u use softsoap cause that the only other thing besides being on my cycle this time that coincides with last month