Hi and welcome to the forums. I am sorry that you are still feeling so sick. It is possible to suffer from pre-eclampsia up to six weeks post-partum, so your symptoms could be related to PE. I can't remember hearing of anyone developing HELLP or continuing to have severe HELLP symptoms after that much time. It took a few months for my liver enzymes to come back down to normal levels, and I think that is relatively common. However, I didn't feel sick and wasn't vomiting after the first week or so.
Extremely high blood pressures can certainly cause terrible headaches, which would make me quite nauseous. What does your doctor say? Is there a chance that you have some sort of infection (fever)? I was a bit slow to recover because I had some retained placenta. Has your doctor checked for that? It is not very likely, but it could happen. It is also possible that you caught some sort of illness, but that probably would have showed up in your blood work or other symptoms.
Daughter born April 2009 at 35 weeks due to Class 1 HELLP