Hi Lucy,
I'm sorry there was a delay in replies.
It can be really tough, when you relapse, to find your footing again. Please know that recovery isn't a straight line and there will be times when you struggle, but that does not negate all of the good moments in your recovery that you've had up until that moment.
That being said, as Emmie suggested - eating disorders can be difficult to navigate alone, and it's important to have a support system in place for moments like this. Are you seeing a therapist or other mental health professional to supervise your recovery? If not, you may want to consider reaching out to someone. I'm not sure where you're located, but if you're in the USA you can find professional help, discussions about relapse and even low cost support of finances are an issue here -
https://www.nationaleatingdisorders.org/help-support
Do you talk about your eating disorder with any friends or family members? Can any of them help support you when you find that you're struggling? If not, you may also consider finding a support group - I know it can be hard to open up to those that are close to us about something like this so having a group of people that are experiencing the same or similar things can be really validating and can help you in tough times.
We also have tons of great options right here, on Teenhelp, if you're having a particularly tough day you may want to reach out to LiveHELP or HelpLINK where you can provide more details to your situation, if you're comfortable, with our amazing Staff. We also have a great new program - LinkUP where you can be matched with a mentor.
You can find information on these other services here -
http://www.teenhelp.org/getadvice/