The symptoms could also be related to your sciatic nerve, this is something that would become more inflamed with weight gain, such as pregnancy and can flare up every now and again. The sciatic nerve exits out through lower vertebrae in back and can cause pain down to the heel or foot.
M.S. is typically diagnosed by a neurologist with an MRI of the brain and cervical spine with gadilinum and also a lumbar puncture.
An EMG is a nerve conduction test that can determine if this is likely something less concerning such as sciatica or more concerning like a central cause as M.S.
Feel free to ask more questions if you have them.
Sometimes just starting with a visit to a doc and having them perform a physical and take a history can alleviate a lot of stress. Like I said this may not be M.S. but because you have recurring symptoms and you are anxious regarding this your best bet is to see someone even if just to alleviate your anxieties.
Sincerely, Jennifer. I hope my answer helped you. If it did please be sure to give me a good rating. If it did not please contact me as I would be happy to help you further.