How bad is my achilles tendonitis?

My Chiropractor said that I have achilles tendinitis in my right foot. I think that part of the reason I have it is because about two years ago I sprained it. Ever since then I have had this painful popping sound when I walk or rotate it. Another reason that I have it is that I have some really bad flat feet. I'm NOT overweight and I am 14. It hurts all the time, even when I sit. She had me go to an orthopedic doctor to get personalized foot supports, hoping that it would decrease the pressure on the achilles tendon. It's been about two weeks now that I have been wearing them, and my foot has slowly gotten worse too the point that I'm on cructches. I can walk on it, but if i walk normally I feel a lot of pain my calf. So I was wondering how bad it is, should I go to a doctor, and what should I do to make it feel better? I have the R.I.C.E. treatment and it still really hurts, but I have only done it for two days. How long should I be on crutches?