Underweight and weakness at 24 years.

Before you read further, let me tell you its quite long.
Can I discuss this with some medical professionals too ?

About me:
-24 year old guy with a 25' waist (thin) !!!
-Height - 5'11
-Weight - about 120 pounds
-Structure - frail
-Mind - Not very alert, but when stomach is ok, sharp and intelligent.

Current Problems:
-Get tired easily/quickly (haemoglobin ok, but at minimum for male of my age - confirmed)
-Low blood pressure (do not remember value)
-Mild & infrequent constipation, gas.
-Low weight, strength, stamina, alertness.
-Noisy and painful movement of joints in fingers, wrists, ankles (urine tests do not indicate possibility of arthiritis)
-Feet and palms get cold easily (perhaps reynauds syndrome)
-Quality of sleep, 5-6 hours, erratic.
-Get weak during dangerous or tense situations. (Adrenal problems ???)
-Low rectal prolapse


Tests:
Endoscopy-ok
Barium meal test-ok
Ultra sound-ok
Thyroid tests-ok
Urine and Blood-ok, except haemoglobin is at minimum.

Past:
Diet in teenage - Poor, lot of fast food, spicy stuff, cola, coffee etc.

I had hyperacidity for sure almost every second day and it seems that I had IBS (due to frequent constipation). It hurt me for 5 years, despite cutting the poor diet. The constipation is almost over for more than 2 years, after I took anti h-pylori medication.

Misc:
Possibility of Gluten or Lactose intolerance ruled out, but not confirmed.

Can anyone suggest what this could mean and how I can get out of this problem(s) ? Cannot be frail and dull at young age. Need to be faster and better.