black stools and loose stools are seen in people taking iron supplements
as your previous delivery was by cesarean section adhesions because of that surgery may be responsible for your pelvic pain
other possible causes are increase pelvic tilt
can occur in second pregnancy
and size of the babies will also increase with increasing parity.
you can go for iron syrup or injections if the symptoms are more troublesome.
try to take analgesics, sleep in left lateral position, avoid prolonged standing and lifting weights,
if pain will not subside even with this better visit your doctor once, get examined and follow her advice.