EP chemotherapy is a two drug protocol containing Etoposide and Cisplatin. Etoposide s major toxicity is myelosuppression ( i.e it decreases blood cell counts) and Cisplatin is notorious for kidney toxicity and electrolyte imbalances. The toxicities of both these drugs is cumulative that is it adds on as the chemotherapy cycles progress. Now feeling of being drained with aches and shortness of breath can be due to anemia secondary to myelosuppression. The muscle aches and weakness may be due to hypokalemia (low serum potassium levels) and/or hypomagnesemia (low magnesium levels). I would suggest that you have your lab investigations including Complete blood counts (CBC) and Renal function tests (RFTs) including electrolytes to see if there is any abnormality which can be rectified. I hope I have answered your query. If you any further questions I will be more than happy to help.