Hi there, well done on the weight loss, amazing! I changed my food range to help with pre diabetes and I lost a stone without planning, colleagues at work kept asking if I was ill. So I tried to add muscle, like you I walked and walked but nothing changed, a friend of mine who is a fitness professional told me walking is great but not for building muscle. I now do weight lifting every other day, I am seeing an improvement in my muscle strength but have a way to go yet. Not sure if that helps, but thats my journey thus far. Good luck, you will get there.
ps Davina McCall has a great, free video via YouTube called ‘top fit’ it’s pretty good and fun.