Hi OP!
I'm a fitness instructor and have been for 4 years, now managing a gym in South Wales.
To start with, congratulations for making the decision to improve your lifestyle! The first step to making a difference is having the courage to make a change.
1. The instructors at your gym will help design a tailor-made program for you to make sure your path to a healthier body is at a safe, measured rate and under their guidence. A good instructor will not leave you to your own devices and leave you to figure it out yourself. By prescribing exercises suitable to your fitness level so don't worry about pounding the treadmill, using a cross-trainer may be more suitable for you. With determination and a positive attitude, you will develop and improve your fitness and lose weight.
2. Have you considered going for a 20-30 min walk instead of jogging? If you are unaccustomed to running (that includes jogging!) then it may be better for your joints to go for a brisk walk instead. Plus you are more likely to achieve a three mile walk than a run at the moment! Failure to complete an exercise leads to disheartenment and ends in giving up. By regular walks and training in the gym, you can build up to jogging.
3. A good gym instructor relishes a project! There is nothing more satisfying than seeing somebody you've advised and guided achieve their goals and celebrating a success. Their first 10 minute run on a treadmill, the first 5lb loss, the day they see a result. Instructors will support you through your journey, always ask them for advice and if you're not sure about anything.
4. Human nature dictates that curiosity and jealousy makes people stare, it doesn't matter if you're a 15 stone ripped bloke deadlifting a small elephant or somebody trying their best to lose weight. I love CrossFit and get stared at when I'm doing my circuits, I've had men leave the weights room when I walk in because they can't stand the thought of training in the same room as a woman! But there was a time I was using a gym because I was two stone overweight and beasting myself on the cross trainer.
Be strong, be determined and never ever let your head go down!
Gym Bunny