Hey you sound like you have alot going on right now.

"what age would they expect a period to become normal?"
well technically your period becomes regular about 3- 4 years after getting it first. Until then, its normal to be irregular.

"and would I be absolutely required to go on the pill of they suggested it?"
many doctors suggest the pill to make the menstrual cycle regular and it does relly help. It also gets your body used to it so it can normalize the period by itself. But you are 17 so they cant really make you do anything. But they would probably really recommend it.

"if I tell my doctor I haven't had my period in a year, would it raise suspicions of an ed (even though it was never regular)? "
missed periods are a classic symptom of an ed but im sure your doctor will check everything else in your body that could be wrong before diagnosing you with ed. However, if they know that you have struggled with ed they might think that could be the reason for it. Explain to them that your period has never been regular and also tell them that you have an eating disorder.

Lying is not the way to go. If you are struggling with an ed tell someone. Please please tell someone. I almost died because of my eating disorder (i'm 17 too btw).

Im glad you said that you gained weight recently, you seem to be on the right path. Please take care of yourself, you are worht it.

I'm so sorry this is so long of a post, I hope it helped at least a little. You can talk to me anytime you feel like it. Let me know how its going.