Welcome to the Forum.  I'll be pleased to comment.  My sense is that your GP is well informed and whomever agreed to give you the PEP was not.  Masturbation of any sort, including ano-rectal masturbation of the sort you describe is generally considered safe sex.  Interestingly, this is the case despite that fact that it is typical for persons engaged in mutual masturbation to get their partner's genital secretions on one another in the course of masturbation.  This is testimony as well to the fact that it is DIRECT, not indirect (i.e like on a partner's hands) sexual penetration that results in most STI, including HIV, transmission and explains why most exposures to persons known to be infected do not lead to infection.

In your case, not only was your exposure safe sex but from what you write, it appears that you do not know that your partner had HIV.  Putting these together, like your GP, I see no reason to continue PEP and would not have recommended it in the first place.  I do not fault you for being concerned but it is always a disappointment when professionals do not use medications correctly for all of the reasons your GP mentioned.  PEP is not only costly but has side effects in some.  I agree with stopping the meds at this time. 

I hope my comments are helpful.  EWH

Actually, most people have cuts and scrapes on their hands and fingers and, despite this, masturbation of the sort you describe has never been associated with risk for HIV.  If I were you, I would not be worried at all.  For that matter, I personally see no medical need for testing.  I realize you will probably test for your own peace of mind but urge you not to worry in the interim.  EWH