First, let's clear up some confusion. You're using two terms which mean many things to many people: libido and sex drive. I'm not sure what you are referring to, so will hazard some guesses.
If you have no interest in sex, that may indicate some conflicting psychological or emotional issues that are hindering you from thinking about sex. After major surgery, many people find themselves questioning their body image, attractiveness, etc. Surgery can have a major psychological impact.
If you're interested in sex in general, but have no desire, that may indicate that you are conflicted about some aspect of sexuality. It's important to differentiate between general sexual desire and desire for partner sex or a sex with particular partner. A first step is to examine whether you are having erections upon awakening. If so, that's usually a good indicator that there's no physiological issue. If, however, you AREN'T having erections upon awakening, or if they're not lasting very long, you should definitely see a urologist to determine whether there's some residual nerve damage from the surgery.
If you're finding you don't think about sex, there's probably a reason. As I said, perhaps you're not feeling very sexy right now, due to the aftermath of the surgery--or perhaps you're feeling conflicted about sex or about your fiancee. These are questions to ask yourself. If you feel conflicted or ambivalent about sex, you may wish to see a counselor who is trained to help people with sexual concerns. One or two visits may enable you to understand your feelings and gain some valuable perspective. Best of luck to you. Dr. J
my girl friend want to have sex bit i cant keep an erection for a long period and i keep stalling and saying that i wont have sex with out an std test first and i dont want her to think tha i am useless in bed and where can i get condoms without my parents finding out