What Causes Lower Abdominal Pain And Constipation After Taking Magnesium Supplements?

Hello doctors..... I am 63 YOA, in excellent health. I take NO medications. Recently a friend talked me into taking 1000mg of Magnesium for joint pain. I did this daily for 2 months. Gradually I started getting lower abdominal pain with constipation so I stopped the magnesium. I have tried laxatives and prune juice to relieve the constipation. However, it then turned into diarreha which lasted 5 or 6 days. It was severe, like every 20 minutes for days. I finally took Imodium 1 dose of immodium to stop it. Know I have stomach cramps with occasional nausea. I m guessing dehydration but I am no means a doctor.. I started Tru Biotics today to try to replenish my good bacteria and was thinking pedialyte. My insurance sucks, 10, 000.00 deductible. I used it once last year for the flu and they raised my premium 100.00/month so here I am on webMD searching for free advice. If you can offer some type of alternative it would be awesome. Thank you in advance and have a great evening. Brenda