Donna, I share some similar worries. The result is either that I am not at all worried about things and don't get them checked out when I should - or, by the time I finally do get myself to the doctor to have them checked, I'm a quivering wreck because to get to that point, it means my anxiety over what might be wrong has exceeded my anxiety over going to the doctor(!!!). As a result, the doctor thinks I'm an anxious mess. But really, allowing myself to get more anxious about whatever the issue is, than I am about going to the doctor, is the only way I will get myself to a doctor's. So that's just how it has to be. (Compare this to my husband, who is ultra logical and calm and just pops to the doctors with no worrying as soon as there is some little thing he wants to get checked...)
Which is all to say... what is going on with you might be nothing at all, or might be something which some simple local estrogen could fix - but it could also be serious. Unscheduled bleeding can be a sign of cancer - of the cervix or of the uterus. If you are scared of doctors, are you up to date on your smear tests? Please don't mess around with getting yourself seen. Take your husband or a friend with you. They can come in with you or wait in reception. Tell reception when you make the appointment that you need extra support and are anxious about doctors. Tell the doctor before explaining anything, too. They might even be able to prescribe you some Valium or beta blockers to take, which your husband can pick up before - just so you can come to your appointment. But don't just leave it and not get it examined....
You mention this fear has gone on for 3 years - did something happen, did you have a traumatic experience at a doctor's?