I m a 17 year old male..... i feel exhausted after 45 mins. of lite workout what could be the reason? whatz the remedy..?

Several reasons: There are several possibilities for this symptom. Would need more information and possibly more tests for a correct diagnosis. Some possibilities, simply, you're out of shape. Or, low vitamin D, low iron, low thyroid, anemia, over training syndrome, heart or lung disease. I would recommend you get in to see a doctor for further evaluation. This is not normal for a health 17yo young man.