Boy -- my name is popular!! Welcome to the boards girl!
First congrats on your accomplishments & learning so far! 110 lbs is no small thing. I also understand your frustration as I'm also stuck and can't drop some bf. From personal experience over the last year (I did 2 bb competitions last year, lost & gained 20 lbs 2 x in 8 months, loaded ephedrine for my second comp, blew up to 20 lbs more than my life average and haven't been able to lose it despite comp-level training & diet....)
1) Yes you can get burnt out on thermos. Just like anythign else you put in your body, especially if it can load your receptors over time -- you should cycle it like every 6-8 weeks. You could either just go off for a period of time or try switching from an ephedrine (ma huang) based thermo to a norephedrine such as Adipokinetix. (Someone please correct me if I"m wrong - I heard that Syntrax was taking the Nore out of the Adipo formula so I don't know what it is now...) If you've been taking thermos for a long time, I suspect they can do bad things -- I'm still trying to understand all that -- I was building my own ECA stack w/ ephedrine, No Doz & aspirin at about 6 ephedrine / day for 4 months, 2 days on, one day off. At the end of 4 months of competition training I was so burnt out I couldn't complete a workout with my trainer. He said he was lifting more than I was just spotting me. You may need to just take some time off from it.
2) If you do the same routine every week, especially if you are compelled to do cardio and you are now at a plateau, probably time to make a complete change in how you train. Your body may need to be shocked a little - force it to adapt to a new training regimen. One thing to remember about making changes in diet & training is that nothing happens overnight - may take 3 weeks to see results, and your diet needs to be tight to see changes in the short term. So sometimes you have to "feel fat" for a few weeks before a change occurs. Frustrating but just the way it is.
As far as motivation, maybe you just need some time off period. You can really get burnt out from over training -- I am also guilty of that (see #1) - trained until I was limping out of the gym 5 nights per week, trainer spotting me to failure sets on everything.
Basically when you start feeling like shit or losing interest in training / diet, that is your body telling you it needs a change - either its not getting enough of somethign or its trying to protect itself from something you are trying to make it do that it doesnt' want.
I also think you have a slight "mental dependence" on your cardio. I understand how good it feels, but maybe try refocusing more on lifting -- you can do a "cardio workout" by keeping your intervals between sets down to 30-45 sec, keep your whole routine intense as hell and an hour or less. I hate doing cardio because I miss the euphoric feelign I get from a balls-to-the-wall lifting session! Also challenge yourself to keep a strictly clean diet for a week, then a month - when you start to see results you actually enjoy doing a strict diet because its more rewarding to feel "lean" than to junk out on that Friday night. Diet is definitely a bigger part of trying to lean out than cardio ever will be, so its a good place to have good discipline and consistency for bigger return on effort.
If you are at a plateau, also remember that your body has gone thru a lot of weight gain and loss, so it may just be shocked right now and trying to hold on to the bf that it has to protect itself from any other large weight changes that may come in the future (it may think its in "survival mode"). It may also be trying to protect itself from the stuff you are putting in, like T3 & clen. I think esp for women, it is hard to continually manipulate your metabolism with foreign substances without having some sort of body response.
Like I said, I'm in the same boat, I've been dealing w/ an extra 20 lbs for 10 months and I've tried everything from clen to holistic dieting. My body just seems to be VERY comfortable at my current weight. I'm not.
You might also get some blood tests done to check your thyroid levels, etc. I don't know -- this holistic nutritionist I worked with for a while said ephedrine can majorly screw up your metabolism and possibly your thyroid. Never hurts to check.
Good luck!