"Feeling really disheartened. Week 4 of no loss. Since I started on the 6th jab I've gone 226, 215, 218, 215, 215. I was ill at the weekend and that combined with feeling utterly shit about the whole thing meant I cheated big style on Sunday for the first time. Potatoes, pudding, cake. You name it, I ate it. Regretted it as I felt like shit, and am back on track now, but I don't know what I'm doing wrong."
There's a clue in Potatoes, pudding, cake. You name it, I ate it 
Weeks 3, 4 and 5 are often weeks where you see little or no loss, even a small gain. Looks to me like what was happening to you - and then you will have sabotaged the whole thing on Sunday.
I'm sorry. It's hard to keep going without any apparent benefit, but that's why last week's chat thread was entitled 'keep on keeping on'
Drink lots of water, get back on track and you should be fine