missed lymphoma or something else??

i am a 29 yr old female. sept of 2010 i was diagnosed with medullary thryoid cancer. i had my thryoid removed as well as a few surrounding lymph nodes. it had not spread beyond the thryoid. since dec of 2010 i have had lots of ear infections, sinus infections, uti, bronchitis, Pneumonia, hand foot and mouth disease, and aBartholin glands cyst. in may of 2011 i noticed lymph nodes in my groin and neck. my thryoid doc did a ct scan of my neck and chest it show alot of nodes were enlarged she sent me to a ENT for biopsy the node he wanted was behind an artary so he did PET scan of my whole body to see if there was anything else where. it showed enlarged nodes in neck under arms pelvic and groin areas all with a metabolic uptake. they did biopsy on one node from groin. lymphoma study came back neg. i have lost 50 pounds this past year i am always tired my whole body hurts i cant eat very much because i will just throw it up. i go back and forth between consapation and diarrhea. i wake up sweating at nite but i feel cold. my husband says my skin is to hot to touch at nite yet i have goose bumps. i run fevers when there seems to bo no reason for it. i have headaches everyday. my potissuam is always low and my liver test one is high but other is normal. my calsationin level is undetcetable so its not thyroid cancer again last week my white blood cell count was moderatly low.my doctors dont seem to know what it is and want to do another biopsy this time in my nec of chest. what could this be and why is it so hard to figure out???? also my lupus test and ra test were neg.