Okay here is my advice to someone in your position:
- Use that MyFitnessPal app to calculate your calories so you can see exactly how you are doing
- Always eat UP to the amount it says don't try to under eat
- drink 8 eight ounce glasses of water a day (your body can hold onto a lot of water weight!)
- Look into HIIT (high intensity interval training), do what you can. That is the only cardio I really approve of.
- WEIGHT TRAINING... look into the book 'New Rules of Lifting for Women'
- When you can, get checked out by the doctor
- Get full nights sleep
What I was told when starting exercise is that what you do for work does not count towards your exercise. Because you will do it enough that your body will get used to it. So either you can up your intensity at work by power/speed walking everywhere, or jog/speed walk with your dog at home.
Now I understand not everyone has the best joints so do what you can and it will eventually get easier. Sometimes my knee kills me and I can't jog... lets just say I have pushed myself so I can speed walk almost as fast as I can jog!
Try doing 'fun' exercises sometimes. The great thing with the internet is there are TONS of videos you can follow along with. Try Zumba, Dancing, Bellydancing, karate, etc. Or get an Xbox + kinect (if you can afford one) and get one of the dance games!
I also am not sure about your financial situation but if it is not that good, you may need to get creative! You can make a lot of your weights from old dufflebags, kittylitter and ziplock bags. Look up sandbag weights.
You really have to be 100% in it to win it. I always say losing weight (or even working out) is 80% determination and 20% physical exertion.
If you do start weight training don't be alarmed if you gain weight, its good! Muscle weighs more than fat. I am looking forward to weight training because than I can eat more!