4 1/2 years out and suddenly gaining! HELP!

I'm 18 years out and went from 247lbs to 128lbs and now I'm 181 lost 15 lbs and trying to get back down to 150 and try to stay there. And it's hard I went back in protein shakes and one meal at supper. It's slowly coming off I give myself a cheat day once every 2 weeks and it is usually a steak house. Good luck to you. It's a awful battle and we carry this battle all our life