Worried about weight gain

Lottie • Mum to 2 beautiful children and 12 angels 👼
I'm 26 weeks pregnant and started off with a BMI of 33 so was told to not gain more than 20lbs (9kg). 
The last few weeks I've really noticed it creep up and I've gained 12lbs already. 
I do go walking every day but in all honesty, that's about as much exercise as I manage between dizziness and SPD. 
Any advice on how to keep it aa under control as possible in the next 14 weeks? 
I can't believe I let this happen :(