What do you mean by lumpy bits?
It's really hard when they up and change on you isn't it? There are a lot of possibilities though. Sometimes we can figure something out, but a lot of the time it just comes and goes and we're none the wiser. I do think as mums sometimes we're a little too hard on ourselves, immediately blaming ourselves - for what we ate, or for doing someting differently or getting something wrong - when in fact it may just be due to the many vaguaries of babydom.
Take care