I'm sorry to read that you suffer so much...it sounds like you may even be having post-traumatic stress syndrome. I'm sure it's a lot more prevalent among the cancer population that we realize. Cancer is a traumatic diagnosis, and ongoing treatments, the worry of recurrence, the twinges that we project to be metastasis, it's not so unusual to have these fears. Cancer is a huge burden but you are not alone.
If I were you I'd do what I could to find a decent therapist, one with the ability to prescribe medication if need be. Don't let yourself sink into the deep dark pit of depression. I've been there and it's worse than anything else I've ever been through. I used antidepressants for 5 yrs and had therapy for the last 2 or so years of that. Last year I began doing something new, drawing and painting and soon after that I felt so much better I terminated the therapy. I've been off the antidepressants since 2004. If you have questions on that subject please ask, I'm sure many of the folks passing through here can chime in on the subject.
One thing my therapist said to me during the times I'd be fatalistic about my cancer diagnosis is, "if the sun were shining, would you sit there waiting for it to rain?" and of course I had to say, "no, that's totally stupid." Worrying is not a good coping mechanism because it's almost always worrying about something that probably won't even happen, and we are projecting our fears onto the future. It's futile.
Cancer is a life changing event and nothing will ever be the same. Believe it not, people get used to anything and eventually adjust. It's natural to have the anxiety you describe, but nobody can live like that for too long, so if it doesn't ease up get professional help.
In the meantime, feel free to vent here!
All the best,
Wendy