Some cancers are detectable with blood tests. I'm assuming your doctor took several blood samples and determined no cancer cells in your blood. I agree that you need a second opinion. When you see another doctor, just have them start at the beginning - don't mention the other doctor and his diagnosis or this new doctor will just concur and agree with the other one. (I made that mistake). I hope you find out what can help - Essiac is supposed to shrink tumors. (Tea or capsule form at health food stores).
I am assuming that the doctor diagnosed you with a lipoma, which is a benign soft tissue tumor that can get quite large. From the Wikipedia site:
"Usually, treatment of a lipoma is not necessary, unless the tumor becomes painful or restricts movement. They are usually removed for cosmetic reasons, if they grow very large, or for histopathology to check that they are not a more dangerous type of tumor such as a liposarcoma.
Lipomas are normally removed by simple excision. This cures the majority of cases, with about 1-2% of lipomas recurring after excision. Liposuction is another option if the lipoma is soft and has a small connective tissue component. Liposuction typically results in less scarring; however, with large lipomas it may fail to remove the entire tumor, which can lead to re-growth.
There are new methods being developed that are supposed to remove the lipomas without scarring. One of them is removal by the use of injection of compounds that trigger lipolysis, such as steroids or phosphatidylcholine.
Lipomas are rarely life-threatening and the common subcutaneous lipomas are not a serious condition. Lipomas growing in internal organs can be more dangerous, for example lipomas in the gastrointestinal tract can cause bleeding, ulceration and painful obstructions. Malignant transformation of lipomas into liposarcomas is very rare and most liposarcomas are not produced from pre-existing benign lesions, although a few cases of malignant transformation have been described for bone and kidney lipomas. It is possible these few reported cases were well-differentiated liposarcomas in which the subtle malignant characteristics were missed when the tumour was first examined. Deep lipomas have a greater tendency to recur than superficial lipomas, because complete surgical removal of deep lipomas is not always possible.["
I would recommend getting a second opinion from another doctor, and probably getting a biopsy to make sure that it is not a liposarcoma. If it is causing that much pain you should probably see if there is any way it could be removed. Many laproscopic surgeries only take 1-3 weeks to recover enough to go back to work (you may still have pain, though), but open (regular) surgery could take 1-2 months before returning to work. I hope this helps.