Andy - I wouldn't have thought you needed to eat extra food. That's more for type 1's on insulin who are trying to make sure they don't go hypo after exercise. You as a type 2 on meds will not go hypo no matter how much exercise you do, so you don't "need" extra food in a medical sense. However, if exercising has made you hungry, as swimming will often do, I don't think you necessarily need to deny yourself food artificially - just try to have something healthy.
Akindrat - a really good starting point at the gym would be a cross trainer (the ones where you move your feet and arms simultaneously). They are kinder on joints than a treadmill when you are carrying extra weight. As you lose a little more weight you could move to a treadmill then and, as someone suggested, keep it at a slow-ish speed but on an incline (adjusted as to how you can manage). Jogging would be very hard on your knees and feet at your current weight. Another good one would be a reclining bike (you sit in the seat like a chair, and your feet doing the peddling are out in front of you). That will be easier on your nether regions than sitting on a normal "saddle type" stationary bike. Rowing machines are good but you may find it easier to keep your feet on the floor, rather than in the stirrup type things provided. If you put your feet in those, it can be hard to achieve a proper rowing form if you have a large stomach. When you have warmed up doing some cardio type exercise like this, you could have a go at some resistance training using the machines. There should always be someone around to show you how to use them. The good thing about these is that being overweight doesn't really make it any more difficult (unlike with cardio). You are working one or two muscle groups at a time, and your overall size is not really an issue. Using these will not make you bulk up like a bodybuilder. That requires intensive work at much much higher weights than you would be using. They will just help you tone, and improve insulin resistance.
Type 2 on Metformin, diagnosed Jan 2013, ultra low carber, Hba1C at diagnosis 8% (64), average BS now between 5 and 6 mmol.