You have not provided sufficient information to make a judgment about this problem. What was the time interval between receipt of oral sex and the appearance of the lesions? Further, it is not clear how a swollen lymph node would lead to an open wound in your genital area. finally, you need to clarify exactly where the lesion/sore is.
I would suggest you see a professional who can evaluate this. One possibility is that the neosporin that you are applying has induced a an allergic reaction.
Perhaps I can add more when you provide more information. EWH