Hello,
Welcome to ehealthforum and thanks for writing
You seem to experience most likely flickering of abdominal muscle and should resolve on it's own when the muscle is given adequate rest. Though the exact diagnosis can only be made after examination by a doctor, if it isnt painful and stops on it's own in few hours to a maximum of two days then it is more likely due to muscle twitches. It can be a side effect of drug abuse,underlying mass,anxiety etc.The possibility of pregnancy seems to be less.
If it persists or you develop any pain or swelling or any new symptom then please seek prompt medical consultation.Avoid any self medication and drink lots of water.Have healthy balanced diet and take a good sleep.
Take care!