Please help me!!

emma • musician & mua
I don’t know what’s going on with me and I don’t know where else to post this so maybe you girls will help me! 
For the past few months, I’ve been getting dizzy and passing out while sitting down. My head starts throbbing and I get a slight headache and I’m out. I know it’s fairly common to pass out when standing up, but it happens when I’m just sitting. When I wake back up from passing out I get a sharp stabbing pain at the base of my skull. My hands shake all the time and people point it out when I’m in class. They always ask if I’m cold or something because my hands constantly shake. 
Just these past 2 weeks, I’ve been sleeping for 15+ hours overnight and could sleep more if I didn’t force myself to wake up. Last night (and day..), I slept 19 hours. I can’t seem to get awake when I know I need to do I just go back to sleep. I don’t know what’s going on. It doctors can’t seem to find any reason for me passing out. My local healthcare systems are known for being the worst and they don’t care about their jobs. My mother has lupus which is an autoimmune disorder so it’s very likely for me to have those disorders as well. Please help me, I’m so stressed and worried about this!!!