Cephalexin Monohydrate and toes

I've been taking Cephalin Monohydrate now for two days: one every hour and my heart seeded up a double (up to 120 beats per minute). I'm taking it tonight cause I afraid I might have a heart attack if my heart beats get faster. I stopped taking now for nine hours and my heart beats are getting back to normal little by little.
Hope this could help you.

I've been taking the medication for three weeks now, 500 mg (I think) twice a day. I've been suffering from a constant gurgling in my stomach, as if from a stomach virus. I'm also experiencing joint pain and some tingling in my fingers and hands, also some pain in toes/feet. Initially I suspected the joint pain could be the onset of arthritis, since it runs in my family. But then I remembered I've been taking this medication for quite a while now; I'm wondering if joint pain could be a side effect?