your doctor might have detected fibroid
in the second scan because fibroids grow in size during pregnancy
due to the effect of hormones,
in case of no symptoms with fibroids we can weight till delivery,
but as you are having severe pain
with your doctor's advice you can take analgesics, adequate hydration and rest which will decrease the pain to some extent,
if not you can go for surgical treatment
like myomectomy, if your doctor suggests.