Well, I don't know the exact answer but maybe I can offer something helpful.  I do know that motivation does not come before action they say--you first have to act--go the gym-then the motivation comes.  Unless you really do not like working out at the gym--I know I don't in which case, find something you do like so you will keep doing it. For me it's running on trails.  I hate treadmills so I have no motivation to do that, but alone on trails in the trees I like. Ask yourself if you really like the gym or there may be some other kind of exercise you prefer and force yourself at first.  Only then comes the motivation, after first forcing yourself and make sure you enjoy the activity! Hope this helps.

Marishka