Got my period back once..but now gaining weight?

Basically I have had Amenorrhea for a year and 3/4. I was never underweight but I did lose about 10 pounds and was restricting for a few months to a year (depending on what you consider restricting). I have also consistently done one cheat day per week so it's not like I wasn't eating (more like Binge/starve). Changed my diet just a little and gained like 7-10 pounds from adding some more carbs, so after a while of still not getting my period, I decided to watch a little more and eat what felt comfortable for me while still making changes.

From the end of May to June 8 (so two weeks), I went to England on a study abroad trip. Wasn't working out, watched what I was eating, but didn't go overboard except for a few days

About a week after I came home, I cheated one day and got my period the next day! June 14th...

It lasted for 7 days so it was definitely a real period and I had breast tenderness and everything...

I am scared that the only reason I got it was because I WASN'T working out, so I started using just the eliptical for running this past month instead of the treadmill. After my period, I slimmed down, but now I can barely fit into some of my jeans...

Is this hormonal weight gain from getting my period? Did anyone experience this when you started getting your cycle again? I keep wondering if it's water weight, it has been going on since last week (I had breast tenderness so I thought it might be ovulation?) Haven'y been eating many starchy carbs from bread or anything, just beans and legumes really...

I just am confused because I don't want to do anything to compromist getting my period but at the same time this is getting ridiculous...

I really want to know if anyone else has had a similar experience?

These are questions for your doctor, really.   However, since periods often disappear when a woman does too much exercise, it's reasonable to assume that when you stopped exercising you got your period back. 

A lot of girls I know change shape when they get their periods and develop curves even if they don't actually gain much weight.  I suppose it's part of the transition from 'girl's body' to 'woman's body'...   If you're still a healthy weight, I wouldn't worry about it.