Hi lybrate-user good afternoon. please not to worry about your weak stamina. It can be increase by the UNANI diets. please take some UNANI diets from the any AYURVEDIC STORE (MAJOON LABUB KABIR 1 TSF IN THE MORNING WITH LUKE WARM MILK AND 1 TSF MAJOON SHABAB-E-KHAAS IN THE EVENING WITH AN APPLE FOR 4 TO 6 MONTHS REGULARLY) if you want to know more information about your query please make a visit at my clinic or chat through Lybrate thanks.
Don't over exert yourself. Eat lot of proteins like cheese, soybean, tofu, porridge, sprouted black grams. Also instead of lifting weights first of all start doing push-ups and chin-ups to increase muscle strength.