Motivation can get you started, and it comes and goes. Its habit and determination that keep you going. Make lifting a part of your lifestyle.
For me I come home from work, I lift, I eat. A lot of people would be bored with my life, but I like it.
And everyone loves newbie gains. After that its slower, and plateaus happens, but there's still progress. You have to learn to accept that the further you go the longer your timeline for change becomes (if that makes sense).