Well done on the weightloss!
Add me on myfitnesspal if you like, same username as here. I'm pretty much in the same boat as you, started last monday, needed to lose 50lbs by August, plus I wanted to lose a stone by half term.
So far I have lost 10lbs. I'm eating around 1200-1400 cals a day, doing couch 2 5k, cycling and walking. I did try shred, lasted 10 mins and hurt my knee!
Have you thought of c25k? It's really good imo, I'm now on week 2.
I lost 4 stone 3 years ago, but have piled it steadily back on since. It IS doable.