Took my son to the docter last week

I've been dealing with this with my 17 year old since last May. She had mono. After 3 months she kept feeling sluggish still, tired, her spleen has been enlarged and was hurting her. Anyway, she just didn't seem to be getting better and started to lose weight. I took her back and they seemed perplexed. They told me that you can test positive for mono for up to a year, but in reality once you get it that it's just always there. We ended up doing all kinds of blood tests and they told me everything was negative. She bickers with her boyfriend a lot, a lot, which I've talked to her about repeatedly. Part of me thinks she's just major stressed about this relationship stuff and that's why she loses the weight. She goes every couple of weeks to see the doc, but I don't know. She was feeling better for awhile and put back on some weight, but now she's not feeling well again.

We go on Wednesday for another follow up and I'm going to push the issue of getting a second opinion or taking her to Children's Hospital. I know they said all her blood work was negative, but why is she still not feeling well?