First of all, don't call it a diet. You've now decided to eat sensibly and healthily so as not to be independant on tablets and their side-effects later on life. To do this you need a plan but you go there slowly by changing certain habits like skimmed milk instead of semi, reducing upto cutting out sugar in teas and coffees, more white meat and fish than red meat, etc
Exercise puts a lot of people off but if you take a walk around the block, you'll feel how much fitter & happier you feel. You'll even look forward to it. Quick walks are a good and free way of keeping fit.
Good luck!