I had the same problem,
thisisme, which is part of the reason I got braces again.. so that I could finally stop! For me, what worked was an appliance they put in the roof of my mouth so I literally could not get my thumb in there comfortably. There is also a special appliance the ortho can install that is designed specifically for thumb sucking called a tongue crib (
http://www.dingusortho.com/images/crib.jpg). It takes a long time to break this habit because we can't escape our thumbs! AND because it's just SO relaxing. I find myself STILL craving it and I've stopped for about 14 months now. The problem is that there is no alternative besides going cold turkey because, even if you only allow yourself to do for like an hour a day, you're letting yourself have that feeling that you know is really good and so you just want more and more. I tried the bitter nail-biter's nail polish, wearing gloves, letting mustard sit on my hands and then not washing with soap ( I
reaaaaally hate mustard!!), but with all of these I failed and found some way around them. My nance was a godsend and the only thing that
forced it out of my mouth. Now my motivation is 1-my teeth are looking amazing!!, 2- I never want to have to STOP thumbsucking ever ever again, and 3- my mouth is shaped totally different now so even if I do put my thumb in, it doesn't fit like it used to, and I DON'T WANT IT TO!
If you really don't think you can do it on your own, talk to your ortho in confidence. It might be a little embarrassing but you would much rather have the tongue crib or something like that to help you. It was
too hard for me to do on my own! If I hadn't needed the nance for correcting a different problem, I would've asked about it.
(This ran on a little long, but I seriously have a loooot of experiencing trying to stop for most of my life. You can always PM me if you have any other questions.)
Good luck!!