I taught aerobics for years. I noticed that those who came to the gym the most tended to be the ones who fizzled out. Establish a routine that works with your body, with your schedule. Over time, once you have found a routine that you enjoy, you can increase it. But in the beginning especially, if you have to fight yourself to get the gym, it will always be a fight. Make it nice for yourself. Work with your preferences, your schedule, your mood. Long term, you will stay with it.