It has been years since I became vegan and if you think about this being a journey and that there is no one to punish you if you go back or take a detour then perhaps it won't seem so difficult.
I had a hard time giving up soda for many years. I would go back to it repeatedly and it was never really what I wanted it to be. It did not make me this or that beautiful person having a lovely life as the commercials like to portray. It ruined my teeth and perhaps bones. It was an ebb and flow til finally I had had enough. THis was not until after I was a vegan for many years. I don't know how I ever thought that that was okay to consume even if it was not an animal.
Becoming vegan did not happen over night. I first was vegetarian for several years, but that did not happen overnight either. I was raised in TX as an unwilling participant in the processing of animals and was entrenched in that culture of you have to have this or you won't live. So, while I never liked it, time is needed for the adjustment and to see how you feel. However, giving up dairy was one of the hardest things, because I would go back and forth until I got some info about what is really in dairy and how it is largely an industry brainwashing....and it is the same with the m*** industry and the almighty *protein* diet recommendations.
I think that going a step backwards is not the end of the world, but if you do so....did you get from it what you really wanted? I daresay that if you diet is well balanced and varied that this might be a mind over matter issue....even with monthly cycles based upon what info might have been pounded into your head as a kid and adult as to what we need to be healthy and/ or strong. I think that it is also hard going against mainstream and the ideas and connections that I need this or that because of what I am feeling. I hope that that makes sense. I have always felt a change in how I feel during that time of the month. However, I don't think that eating non-vegan is going to make me feel better. I usually am very tired the first day or day before. Well, my body is going through some pretty amazing hormonal and dramatic changes. I allow for that to just be...and well accommodate with a nap if I can.
Hope that helps you to be easy on yourself and if you go back to prior diet choices, then so be it. THinking of it is a journey that some people are born in the right place, other travel to the desired destination by many different routes. Some follow a short cut, while others may wander all over the world trying to find there way to the same place.