I've been diagnosed with hypocalcemia. Will I lose a lot of weight?

No. Most common causes of hypocalcemia (low blood calcium level) are vit d deficiency, chronic kidney disease, and hypoparathroidism. Hypocalcemia can be associated with increased urinary frequency and water loss which 'may' cause some minor weight loss (a few pounds at most).
Very unlikely. Hypercalcemia can cause hypercalciuria (excess calcium excretion into urine) which results in higher urine output and may lead to weight loss.