I personally like SparkPeople. I use pretty much everything there, they have a lot of motivational tools and here's some decent (you need an account to see links) that you can start with at home.
I totally know what you mean about going to a gym. I don't. I do what I can at home, and when I got bored with that, I found a bike/running trail near my home that is mostly in the woods and typically semi-private, and used that to start a 5k (walk/run interval) training program with the Zombies, Run! app. I highly recommend it, it's kinda like role playing while you run to keep it entertaining and motivating. When I first started, I sucked at running. Sometimes I would have to walk when it said run. But it gets better. Your body needs time to adjust to using oxygen more efficiently for exercise, especially in your case with asthma, I would imagine.
If you're serious about losing weight though, I would focus a lot on diet and just add in exercise gradually. Focus on one or two small goals at a time, don't get too hung up on the overall picture, but just focusing on one small change and sticking to it until you genuinely feel you've mastered it and made it a habit, then moving on to the next.
Once I started exercising, I found it motivating to put up a sheet of paper on the wall near my desk (or wherever you spend a lot of your time and are guaranteed to look at it everyday), with my workout plan for each day that week. Check the days off as you complete them. Visually seeing the effort that you've put in every day is motivation to keep up with it.
I have this quote at the top of every schedule: Your workouts are important meetings you've scheduled with yourself. Bosses don't cancel. Maybe you could do something similar with something that motivates you. I get pride from seeing how many consecutive days/weeks/months I can maintain my daily goals without excuses.
By the way, fitness is pretty much use it or lose it, especially with cardio, so keep that in mind to motivate you as well.
One of the best studies of the effects of detraining on recently acquired fitness gains found that VO2 max gains (a person’s maximum capacity to take in, transport, and use oxygen during exercise) that were made in the last two months are completely lost after four weeks of inactivity .
Don't over do it. I started feeling pretty confident after a few walk/run intervals and overestimated myself and ended up injuring my leg (not from a fall or anything, mind you, just overstraining it), which made working out nearly impossible for a couple weeks. I pretty much had to start over, for the reason above. Don't do it, trust me, it's a bummer.
This is just a personal preference, but keep track of your progress with strength, endurance and speed, not your weight loss. I find obsessing over the scale to hurt rather than help. The point should be to be fit, not a magical number on the scale that no one else sees anyway.
If you need a workout/accountability buddy or someone to talk to about it or anything, feel free to PM me anytime.