Prescribed Flexeril 10 mg/3 times a day for back and neck pain an...

Prescribed Flexeril 10 mg/3 times a day for back and neck pain and stiffness. I had no relief with one tablet, so yesterday I took 2 tablets at noon, then another tablet before bed. Today my muscles are looser, but I have a strange tingling and numbness sensation on my left side. It's affecting the left side of my upper and lower lip and face, left shoulder, left arm and fingers and left leg. It's not painful but I am a bit scared. The pill should only last 4-5 hours and it's now been 10 hours since that last bedtime dose. So why am I still feeling this effect and when will it go away? And I am supposed to take 3 a day for a month?! I am not sure if I will be taking anymore.