Working Too Much

Few days ago I did a night shift then another late shift the following day. I haven't done this type of shift and I thought it will be bad but actually I was perfectly OK and did not feel tired at all. Since agency shifts is very popular here in Australia for extra money I am doing loads right now. My aim is to do at least 32-48 hours every forthnight in top of my 76 hours full time job. I know it is too much but I still have 2-3 days off every week since we are doing a 12 hour shifts. Lord please give me more strength.