When i do something and i am bent over for quite some time immediately when i get up i have pain in the lower abdomen. it also hurts when i lie down. the pain is deep sharp and goes away quickly?

Frequent or recurrent pain, is not something a young 18 year old should be contending with, without knowing the cause. One needs to see the PCP for a Complete Medical Evaluation: History, Physical, Laboratory Investigation and Imaging studies if indicated. Knowledge is power and once empowered One can make choices and decisions to keep One healthy and pain free.