Great for getting out there. Taking the first step is often the hardest and keeping motivated is difficult.
I'm an army reservist / personal trainer and dad of 1 (not so) small toddler.
My first bit of advice would be do NOT replace your scales and don't get any measures. Trust me you'll weigh yourself get upset and comfort eat. I do it, my wife does it and everybody I know in the world has done it.
Go by how you feel and how you look in the mirror.
Not to mention scales are misleading as you can put on muscle faster than losing fat which obviously increases your weight even though you're actually fitter and healthier.
As carrie74 says HIIT (High Intensity Interval Training) is a great way to blast up that fitness curve. Here's a basic beginner sample session;
30 seconds exercise 30 seconds rest.
- Burpees
- Press ups
- Squats
- Sit ups
- Lunges
Repeat 4 times. (20 minutes total).
You can introduce weights as you get fitter. There's loads of videos on youtube (including myself) and I've got a massive list of them too.
To help boost your motivation I'll tell you about myself a few years ago. When I decided to join the Army Reserve I could barely do a press up. My mile and a half time was 13 minutes and I could just about manage the 50 sit ups.
(standard Army fitness required for a male is 44 press ups in 2 mins, 50 sit ups in 2 mins and for infantry, at the time, 12m30 1.5 mile).
Like you I often felt like death after doing any exercise and struggled after 10 continuous minutes, despite being very active and very fit during school.
I set myself a goal. To do the 44 press ups, 50 sit ups and do a 10min30 mile and a half (most infanteers can achieve this and is regarded as the real unofficial respectful pass time).
So I would say to you, set yourself a goal. Is it to fit into your jeans better? Then great. Or maybe set yourself a fitness target? Running 5k continuously for example.
Then break that goal down. So I could do 5 press ups in one go. I needed to get to 44. Seems a long disheartening way! So start by trying to get to 7. 2 more doesn't sound as much as 39 (because y'know, it isn't).
So I did 7. Then try to get to 9. I did 9. Try to get to 11. You get the picture. This wasn't done overnight, it took the best part of a month. However once you get going you can suddenly take bigger and bigger jumps. So by 13 I could then do 18. Then I could do 24.
(I approached the other tests in the same way).
Fast forward 3 months to the selection (which is now 3 years ago) and I remember doing between 60-70 press ups in 2 minutes, over 70 sit ups and I achieved a 9minute27second mile and a half.
Just a note to improve your running times - do a load of squats. I started doing at least 30-50 squats a day as well as other leg workouts. Increasing your leg strength helps take the pressure of your cardiovascular system.
I remember reading (I can never find the stat again) something like for every extra 5kg (or might have been 10kg) your legs can lift you can knock 1-2 seconds off your stride pace (in other words your legs move quicker which makes sense if they're stronger).
The point is your cardio system only takes you so far. You need the leg muscle endurance as well. Whilst just running will get you there, it will improve far quicker by doing squats, lunges etc.
Other things that may help keep you motivated and try other things are joining clubs if that's possible for you. A friend of mine started working at a bike shop even though she had never ridden a bike before. She learnt, and after 3 months was cycling in excess of 40 miles every weekend. Okay she wasn't leading the pack but she was out there, improving and being supported by people doing something she would never have done on her own.
Even if it's just taking your children out, other people will help you and keep you going. :-)