Thyroid problems and weiht loss

hi I've recently had a hemityroidectomy and and due to have a total in the very near future since my surgey I've been struggling to lose weight and if I slip slightly on my diet I'm gaining so fast, is there anyone out there that's in this situation or has thyroid problems such a hypo etc and has successfully lost substantial amounts of weight if so what's your diet? Would you share? Many thanks