You can learn exercises which you can do even with your back problem. Also
the diet should contain more of green leafy vegetables, fruits
and protein
and less of spaghetti, potato etc. I suggest you eat frequent small meals and stop counting calories. It is best to eat lots of fruits and non-starchy green veggies, go slow on fats, eat carbohydrates in moderation and increase your protein intake (lean cuts, whites of eggs etc).