Kidney infections, kidney stones, cramps, and blood in the urine
are all interrelated.
A stone can cause bleeding, crampy pain, and infection. An infection can cause bleeding and crampy pain with or without a stone.
It's certainly possible that you're passing a stone. It's also possible that blood has formed a clot and the clot is causing a blockage and subsequent pain.
The best bet is to take whatever antibiotics you've been given, stay well hydrated, and give it a few days. If the symptoms persist, see your doctor again.