Is Methycobal Pill Safe To Have For Tiredness?

Hello Dr! I am a 37 year old Asian male. Height 184 CM and weight 84 Kgs. I try to exercise but very soon get tired, Even a short walk of 2 kilometres make me sleepy and tired for the rest of the day. My blood tests are normal but for HG of 17.2 and slightly higher levels of creatinine. I was diagnosed with low B12 vitamin but got injections and got the levels up and above 200, now I am taking Methycobal pills for the last 15 days but still the tiredness doesnt seem to go. I am ok if I am not exercising. Plz help