I am glad that you asked us a question here and we will try out best to answer it.
It seems that you may actually have two disorders rather than just one.
The pain in the abdomen could be due to various causes. You should consult your doctor and preferably a gastroenterologist for the symptoms you are having.
You need to consult a doctor to rule out gastroenteritis, food poisoning, any abdominal infections and stones as you have already pointed out in your post
The further plan of management would involve -
'-Blood tests including full blood count, electrolytes, urea, creatinine, liver function tests, pregnancy test and lipase.
-Imaging including X-ray and plain films of the abdomen
If diagnosis remains unclear after history, examination and basic investigations as above then more advanced investigations may reveal a diagnosis. These as such would include
-Computed Tomography of the abdomen/pelvis
-Abdominal or pelvic ultrasound
-Endoscopy and colonoscopy'
On the other hand for the pain the legs, please see your general physician who may be able to examine and treat you or else recommend you to visit an orthopedician or neurologist for the pain.
Let us know about what your doctor advises and if you need any further information.