how can i not feel disheartened

i've put on more weight, my stomach is potruding through my t shirts now.....years ago i got quite overweight because of an unhealthy lifestyle, i got diabetes type 2...so i worked hard on myself, went swimming regularly, watched my diet and lost 4 stone........so i did well all by myself, my own work.

but now ive gained about 2 stone and i'm not happy with myself and know i have to do something about it again....ive not been swimming for over 6 months....what can i do?