When can I stop worrying?

Last year, following a routine mammogram,  I was diagnosed with cancer in both breasts.  After numerous scans etc - underwent mastectomy of left breast and lumpectomy on right.  Then had radiotherapy and now on hormone drug for 5 years. Apparently,  lymph nodes clear. I should feel lucky - after all it got caught early enough to be treated.  So why am I now turning into a hypochondriac? I worry about every strange pain or ache - my doctor has suggested blood tests as I am so concerned.  I don't want to feel like this. This is really not like me and I so want to just be me again. Feeling so low a lot of the time.