Hi there, thanks for posting this ! Here are some things that motivate me:

- Extreme anger that comes from every other aspect of my life (people at work, lack of people in my life, my eternal psychopathology) ... I'm able to channel that anger and all the other negative emotions into an unwavering determination and devotion to my fitness. Even while in the gym, I lift those extra few lbs with the help of that anger. Believe it or not, while I'm lifting, I actually remind myself of the negative events from my past (being rejected by women, being mistreated by family, being ridiculed at work, being bullied as a child, etc).
- Seeing progress (my body changing shape). Not only with exercise, but with anything, when someone sees their efforts paying off, it helps motivate them to do more and get to the next level. The key is once you start exercising, GIVE IT TIME, AND STICK TO IT ! You WILL SEE RESULTS. Those results will then trigger the positive reinforcement cycle: progress -> motivation -> more progress -> more motivation, and so on.

Some tips:
- Start off as slowly as you'd like. No need to figure this out overnight. If you overwhelm yourself when you start off, you might get the wrong impression about the activity and give it up when in fact all you needed to do was to take it easy, and your body will say, "Whoa ! I can't do this anymore. This is too hard.", and you'll give up. Instead, start with baby steps, and over time, you will definitely get stronger and fitter and naturally feel the desire and ability to get to the next level.
- Explore different types of exercise. It's needless to say that different people enjoy activities: Try biking, hiking, walking, jogging/running, swimming, lifting light weights, yoga, pilates, kickboxing, whatever. Maybe also the group classes you mentioned. Try a little bit of different activities (whatever interests you), and figure out what you like doing. Let's face it - if you don't enjoy it, chances are ... you won't continue doing it.
- Whenever you do start exercising, if possible, do also take nutrition into account ... a lot of times, the benefits of exercise can be multiplied when done in conjunction with a good diet.

Fitness is my religion, I'm studying to be a certified fitness trainer, and I have trained many people in the past, so I have some experience with this stuff.

Feel free to PM me with any questions ! I'm sure you'll find something you enjoy or even love doing