Oh my you have been through the ringer haven't you? I feel so bad for you :( at a young age when you shouldn't have to be worrying about anything other than school. It could be the septic shock that was a contributor to your problems, I think that's what happened with me but when I was 29.
Have you seen an autonomic specialist? I think you really should and get complete testing such as Vanderbilt, Mayo or Cleveland clinic. They will check for everything in your ANS system such as Is_something_wrong has recommended.
I have ANS dysfunction and my bp/hr rides rollercoasters daily; it's crazy and I can go from 60 (my pacemaker is set at that rate) to 195 in a blink....most of us with ANS problems are this way...there really is no set in stone thing for ans issues; only what some may experience - you could have a mix of POTS, NCS, OI etc plus some auto immune stuff thrown in there such as I do.
here's some info on Autonomic Nervous system -
http://www.medhelp.org/health_pages/Neurological-Disorders/Autonomic-Dysfunction-FAQ/show/181?cid=196
and dr's in your area who can diagnose & help treat you -
http://www.medhelp.org/health_pages/Neurological-Disorders/Dysautonomia-Specialists/show/717?cid=196
I do see the children's heart institute in VA near you that does testing - they have quite a few locations in VA, so you may get some help there http://www.childrensheartinstitute.org/