how to deal with putting on weight again

years ago i was very fat and had to do something about it, so i dieted and did regular swimming at the gym and lost nearly 4 stone and became slim, such an achievment for me but now about a stone and a half has crept back on my stomach again, ive put on weight and feel disheartened about it...as i have to lose weight again now....i must work on myself again....but it will take time to lose the weight.

any thoughts?