Well since you are on a mental health forum and do not report having cancer,, the first question to you is what medications you take. Depakote, e.g., causes hair loss in many people. Geodon does, to a lesser extent. List your medications and for each, read abouts the side effects it causes on rxlist. I am surprised the GP didn't do that. Do you have a pdoc? If you have a pdoc, and are taking psych meds which are known to cause a wide variety of side effects, some common, such as weight gain, and some rare, such as weight loss, then if you experience a sudden anything, your first response should be to report it to the pdoc, not GP. Whoever prescribes most of your meds, be it an endocrinologist, neurologist, or pdoc should be the first person to learn of any unusual changes.

ok, so assuming that it is not a medication side effect, the next step is to clear up your mind, which currently is very seriously messed up. E.g. that talk about other people thinking that you are a saint and that your guilt increases from your realizing that you are fooling them - all of that should go down the drain ASAP. Given your habits, you should, for now, regard them all as a neutral activity you choose to engage in in your private time. Since you do not owe others reports on what you do with your private time, other people have no right to create any sort of expectation of what you choose to do in your private time, from picking your nose to running a marathon, you cannot, by definition, disappoint and much less fool them.

masturbation used to be considered highly harmful to men, and men used to be believed, by the medical community back then, to have a syrictly rationed lifetime supply of semen. All sorts of things, not excluding adolescent acne, used to e attributed to masturbation, but later such connections were disproved. It is unclear whether the hair loss connection is one of those scary tales given the current revived attention to masturbation or has some basis in solid science. You may simply, as Webgoji mentioned, have inherited the genes of early baldness. How are or were your male relatives in that department is another relevant question your GP forgot to ask...

Re controlling your thoughts - before you attempt to control your fantasy life, which is difficult, you should clear up your irrational beliefs (see above), which should be easy. Once you are free from the feelings of shame, guilt, and being out of control, you will be a much stronger and more grounded man who would then be able to say to himself: "boy, it feels good but I better call it a day for now because I need to leave for an appointment I can't miss. That is ok, as there will be another time."

Also, you might be feeling some rush from living what you believe is a double life. Once you realize that you don't and once you take your habits off their twisted pedestal and onto the ground of fairly mundane things you do, you migjt feel less compulsion in the absence of that extra rush.

Finally, try using the time you spend being aroused but not physically masturbating by using something creative or productive. Channel the energy, so to speak.