Your doctor will probably be able to give you an emergency ultrasound so I would call them asap. Even if (hopefully) everything is fine, you need to talk to them about what could be causing this pain and bleeding.
I am sure if You were 4 months pregnant and already had a child You would be certain by now if You were pregnant and You would have started to show slightly and had more signs. However regardless the pain is not normal You are experiencing You need to see a doctor
Hi:-) Pregnancy, Blood, and Sharp pains does not equal a good sign. Being that you are so far along you REALLY need to see a DR not just in case of complications, the baby also need proper prenatal care. My advice to you is call your DR ASAP before things possibly get worse. Good luck! I will keep my fingers crossed for you:-)
Call your doctor and schedule an emergency visit. If you are pregnant and bleeding - it could be a concern! Plus the sharp pain.....