How do I know when I should workout (should I do it when I am feeling exhausted or in a lot of pain and what should I do)? 

Listen to your body’s signals. If you are very exhausted or in severe pain, do not feel you have to exercise. This is your body’s way of telling you that you should rest and recover. This takes willpower to do because we often feel we will lose all of our progress with our fitness or that we are not strong or tough enough if we don’t push ourselves through these times, but this will only cause you to be more fatigued and in more pain for a longer period of time afterwards, so it is really counterproductive. Allow yourself to rest when you need it. Please don’t feel guilty, this will just stress out your body more! If you must exercise do a light stretch routine instead. Wait until you are feeling moderately better to jump back into your exercise routine. If you have enough energy to do daily tasks then you should be fine to do one of my workouts, but if you do not, then just rest until you do.