Maybe you don't need to have a set number of days per week...some weeks you might visit more, others less. Just do what feels right at the time and be true to yourself ie consider how you're feeling at the time. If you have more time and energy one day say, "oh I think I'll drive over and see mum", or if you're feeling particularly tired and want a rest say, "I think I'll give it a miss today and read my book in bed instead". It is about keeping yourself well and two of the best ways you can do this is by accepting you are doing what you can and by not feeling guilty if you know you need to have a rest or meet a friend for coffee or do whatever it is you would like to do for yourself if you're a bit run down instead of forcing a visit when you really don't feel like it. Either way, it is okay. Your mum, if she were in her right mind, would want you to feel happy and that you are visiting her because and when you want to rather than when you would really rather not due to fatigue.