had thyroid follicular cancer op 11 years ago. now suddenly i have develloped low calcium levels ple

hi-i am in the uk, england
quick history, i had a massive goitre 1995-2001, which eventually started twisting my windpipe, so at that point i had emergency surgery aug 2001 to remove goitre- and afterwards the doctors realised it was a follicular carcinoma, but they had only took the (R) thyroid and isthmus out, as they only thought it was a goitre. afterwards i have been treated by "watchful waiting" by surgeon and endocrinologist. my bloods have always been fine. i take 150mcg thyroxine and 50mcg levothyronine a day. always been fine.........here is my current issue................................
now past few weeks i have felt unwell. my docs did bloods and they found that my calcium level is only 1.9 mmols ( uk ref range). this aparantly is low. so now i am worried . today my doctors repeated my bloods and have checked my calcium and parathyroid levels, i am waiting for those results .
i am worried about what is causing my calcium to suddenly get low 11 years after surgery. i am worried basically cos i think that i am getting a recurrence of my thyroid cancer, or some parathyroid cancer involvement. please help me, i need advice . god bless x maria