It's hard documenting things. I never used to do it until I got f'ed over at work one day.

If you have any emails praising you for your work, save them to a separate email folder—even if they're a simple, "thanks for the help!" If you've got tons of those emails, then it starts to prove that you're appreciated by your colleagues and that your work really DOES matter, that it's integral to what you, your colleagues, and your company as a whole are doing. You want to prove that you're needed, and having solid evidence (i.e., email messages) is hard to dispute.

If your coworkers are willing to vouch for you, don't be afraid to approach them. Worst case, they don't help and you're stuck in the same boat. Best case, they help you out and you get the recognition that you deserve.

If someone approached me asking for help, I would be more than happy to help with whatever it is, as long as that person didn't burn bridges with me. I will genuinely try to the best of my ability to help, but I will always be honest. So expect honesty from your coworkers if you ask for help.