Lymphoma or something else?

Hi, my 22 year old sister hasn't been feeling well the past couple of months. She is caucasian, about 5'4, 180 lbs. She currently has high BP, which she takes BP meds for, and also has been diagnosed with possible Irritable bowel syndrome. She works as a substitute teacher. She has fluctuating constipation and diarrhea often, but usually diarrhea. She takes immodium regulary for the diarrhea.  About a month and a half ago, she noticed the right side of her neck was very swollen. She thought she may just have an infection, and didn't think anything of it as it went away a few days later. This past week, she awoke to find it very swollen again. I'm an LPN and felt of her neck and realized she was swollen in her lymph node area, and told her to see her doctor. She seen her family doctor who ran some blood work on her and told my sister she wasn't sure what was going on, but she would send her to an infectious disease doctor for a workup. My sister seen the infectious disease doctor. He felt of her neck and told her it could be an infection, but he wasn't sure either. He wrote her antibiotics and said to come back in two weeks. The antibiotics did not help. Her liver enzymes have been elevated for several months as well (was found on routine bloodwork) which concerned her family doctor, & the infectious disease doctor. She was tested for hepatitis, HIV, AIDS, mono, & CMV. All were ngative.  She says the swollen area is very tender to the touch. It is getting difficult for her to swallow and it bothers her when she drinks soda. Does this sound like some sort of lymphoma or metastic activity going on? What could be some other causes of swelling in the lymph node area? Could her IBS and constant Immodium use be a factor? Thank you...