First off, losing 20 lbs is amazing. Well done you! You should celebrate that! Can you think of anything that weighs 20 lbs and how heavy they are? Go find random books, put them on the scale until they add up to 20 lbs - and try carrying around for a while. Its not pleasant to carry that much around on your back, so to have lost that is wonderful!
I agree whole heartily on the 'do exercise you love' - and actually, just getting off the couch and doing any sort activity counts- cleaning, gardening, getting off the bus 3 stops early, walking to the shops instead of taking a taxi and then carrying your groceries home, going to the clubs and dancing for 3 hours straight- whatever tickles your fancy.
I hate things like treadmills, stationary bikes, etc- Blah!! I am bored within 0.00001 seconds.
These days, I get 99% of my activity through cycling to work - the 13 minutes there and 18 minutes back (up a hill) adds up to 31 minutes a day of activity and I'm commuting, something I have to do anyways and I quite enjoy it actually- I love getting to work with fresh air pumped through my lungs!
I also do tons of weeding, turning over of compost, etc in the allotment and that's all activity and I'm not sitting on my bum. Plus the reward is all kinds of healthy vegetables to eat!
So I highly recommend finding something you enjoy- Kayaking, Hill Walking, Salsa Dancing, Gardening, Sailing, Gorge Jumping, Trampolining, Tae Kwon Do, Ballet, Rowing, Golf, Curling, Handball!?!
Also, agree if you're doing a lot of exercise, you will need to eat - I'm surprised you're not chewing your arm off trying to do that much exercise and not eating enough. Those stairclimber calorie burners are notoriously incorrect, get a heart rate monitor if you really want to count the calories burnt properly.
Also, a huge thing- make sure you're being whole accurate and honest about your portion sizes. Actually weighing and measuring your food makes a huge difference and 99% of the time we are eating more than what we think we are.
Disclaimer: (Feel free to take what I say with a grain of salt- but I do have a bit of experience with this stuff!) I'm hardly a poster child for healthy weight and exercise. I've struggled all my life with it. Ups and downs and in-between. I weigh far far far far more than I should, but I'm on the weight loss journey - a very, very, very, very slow one at that, taken me 2.5 years to lose what I have. I go off track sometimes- travelling, meals out, going out to the pubs, and eat and drink too much. I'm a roller coaster of weight loss- I also can't exercise as much as I should, I have an autoimmune condition that causes lots of pain so I do struggle sometimes. Still my aim is to fit activity (not exercise, I can't call it that, because my mind goes- "!blah!!boring!!!) into my life and to eat as healthy as possible. I'm getting there. I'm almost into the 'overweight' category and that will be amazing, considering I was in the morbidly obsese one. People would probably find that horrible to be excited to get into the overweight category. Not me! So hey ho!
Good luck!!!