Just noticed your post by accident-- it got buried and unnoticed.
Probably your situation is "just the way you are" and no pathology is involved, but:
Your description is vaguely reminiscent of Marfan's Syndrome-- Abe Lincoln may well have had it. It's genetic and carries certain correctable problems with eyes and aortic aneurysm, and other non-correctable things like lax joints prone to dislocations & ligament injuries.
Thin body plus hypotension also suggests certain adrenal problems that are easily checked with stimulation tests. Full blown Addison's Disease usually comes on more or less suddenly and also usually associated with nausea/vomiting, but "borderline cases" do exist and have to be looked for specifically with testing.
If those aren't your problems, then you're in luck! Just go to the weight loss section here and go out of your way to eat all the things they're saying not to eat there