Weight and SR

I'm sure this is a very common question here, but here goes!
I have been diagnosed with T2 for just over a year.
I have taken Metformin from day 1 - with all the associated tummy problems!
Last month I was changed to slow release and although not perfect it certainly suits me far better.
I am also over weight and need to lose about 4 stone.
I am in my late 50s, work part-time and have recently joined a gym to increase the exercise I do.
But ... in the last month I have started to put on weight - it does tie in with starting the slow release, but I'm not sure if this is a common side effect.
Any ideas or any suggestions with the weight problem?
I'd be very grateful!
Thank you,

I don't count calories as much as carbs.
My diabetes has been quite unstable, but I have found that by eating up to only 50g of carbs a day it really has helped bring down my readings.
A typical day:
breakfast: boiled egg or ham omelette
lunch: either soup or salad with chicken or ham (lettuce, tomato and pepper) oh yes, and a little light mayo
dinner: invariably meat or fish with two or three veg.
I will have either a slice of bread for breakfast of a couple of potatoes with dinner - depends on the menu!
That's the general weekday look
Thanks for taking the time to reply.