Even though I've stopped consuming empty calories from alcohol I've gained weight since quitting, why is this happening?

Increase eating. Eating may be filling the void left by alcohol, find other ways to feel good, regular exercise, getting out house, being with "healthy people".
Maybe a new problem? Usually, one continues to gain weight because of eating or drinking other calories ... And is still taking more calories than he uses in one day. For example, if one was getting 400 excess calories per day while on alcohol, and now getting 100 excess calories per day off alcohol, he will still gain weight due to the 100 excess daily calories. A doctor can evaluate & rule out new medical problems.