Shell Doesn't sound like you have any problems with feeding to me. Maybe just tell you MIL that he is in the 75th percentile of weight for his age (or whatever it actually is) and that as long as he is gaining 150gms a week the MCHN says he is doing wonderfully. You are going to have to have the conversation as DH's don't tend to know how to communicate with their mother's about childrearing. Maybe even give her some written instructions. Politely say this is how I'd like it to be for a week and then ask for her feedback on how it went. Each time she suggests something different just tell her that things have changed since she was a mother, generally for the worse and research indicates your way - even if you don't have the proof at hand. I feel for you having to return to work after 11 weeks. I went back after 4 motnhs with DS and exclusively BF for a further 2 months and continued to BF with part formula during the day for another 2 months and then from 8 months to 14 months I BF when he was with me. Gave up at 14 months because I wanted him not to be dependent on me for night time feeds - he still wasn't sleeping through and it was doing my head in.
As for me - I'm geting better with this whole thing. Talked at length with DH the other night, explained how I was feeling, said things but prefaced with I'm not saying that I couldn't work out how else to explain my feelings so to listen carefully to what I was saying between the lines... it worked out great. Now that I'm letting the communication occur. I've had a super productive day on my first day with both DS and DD at home I have done more in one day than I was doing all week - at least that is how it seems. DD is sleeping for 1-2 hours in the arvo in her cot . Now to get myself to do the night time cot settle.
Speaking of which she has just woken - gotta dash.