I took about a year to become vegan from vegetarian. and even after that for about 6 mo. I ate honey, not yet understanding what the problem with it was.
Originally I tried to eat only french fries, because I didn’t know how to cook, and it made me very sick, hence the long transition from vegetarian to vegan, rather than straight vegan.
In fact, I would say this is the biggest hurdle, cooking. You will fail hard if you try to junk food diet it, at least at first. There are so many recipes on the web, and great books like the Veganomicon, Simply Vegan, etc. Perhaps it didn’t work last time because of that. (Or was it the allure of dairy? That tends to make things rough too.)
So try to experiment. Try making seitan, buying tempeh, and use tofu in various dishes. If need be, you can have a non-vegan or even non-vegetarian day for awhile.
By the way, the two books I mentioned are great. The Veganomicon has an awesome seitan recipe, and a divine pot pie recipe. Simply Vegan has great, cheap meals.
But definitely, I realised pretty early on that you have to learn to cook to be vegan. Less so now, but you’ll spend a fortune otherwise.
Substitutes that might help you: Honey=agave nectar; eggs (for binding in meals) =egg replacer by Ener-G or Bob’s Red Mill, or 1 tblsp ground flax seeds (you’ll need a coffee grinder, they are cheap,) 3 tblsps water, or 1 banana, or applesauce (I forget the amount per egg);cheese=tofutti for slices, vegourmet for block (and is great grated, but struggles to melt in the oven. Melts well in the microwave), daiya for shredded (melts really well, but I like the taste of vegourmet better); there’s even buttermilk replacements you can look up involving lemon juice and soy milk. Though I have never tried this. I never use buttermilk.
Good luck! Even if you can’t become vegan, remember, even lessening the amount of meat/eggs/dairy/etc in your diet is a step in the right direction.