Hi welcome to Health care magic forum.
Thanks for choosing H.C.M.F.
As you describe your son is of five and half years age, and is under weight and height. He is feeling breath less and profuse sweating
. At some time doctors told the B.P. is a bit high, and there are appearent veins on the chest.
If i am not wrong there must be a cardiac problem with him. the other possibility is hypothyroidism
. I advise you to consult a cardiologist
for diagnosis and treatment.
Wishing for a quick and complete recovery.