@happygertie
When that feeling comes to me (and it does) I try to think that I have two options - do nothing, carry on the way I am and definitely stay as big or get bigger, or do something. Time is going to pass whichever option you choose, and in a year's time do you want to be in the same position only kicking yourself because you didn't take this chance, or do you want things to be different?
Don't think about the end goal in terms of weight and how much you've got to lose, your goal is a daily one and it's to eat healthily and treat your body well, giving it all the things it needs - nutritionally rich food in sensible portions, plenty of water, good sleep and a bit of exercise.
You can definitely do it, one day at a time.
And don't worry if 2.5mg doesn't do much, it's not really supposed to - I lost 4lbs in the first four weeks and then 6lbs in my first week on 5mg. So don't give up too early, just play it cool, treat your body well and be curious about what happens to the numbers. They are not the be all and end all.