Cephalexin can be taken in patients who have renal impairment (kidney disease. But the frequency of administration needs to be reduced according to the renal function. The frequency is reduced to 2-3 times per day depending upon the renal function. Cephalexin is an antibiotic and can cause alteration in bowel moments. As you have additional renal impairment, care has to be taken to avoid dehydration. Electrolyte imbalances may cause weakness. I would recommend you to consult your nephrologist and get yourself a serum electrolyte investigation done. This would rule out any electrolyte abnormality contributing to your sluggishness. I hope the above information helps you. Thank you fro writing into healthcaremagic. Have a nice day.