I will go, and I will do it with an outwardly cheerful demeanour- I just feel a bit crap about it and wondered if that was a reasonable reaction!
This sounds ... interesting. I'd want to understand why my husband of eight years wants me to do anything that I am not 100% keen to do, at any time, never mind ten weeks after giving birth. A lot would depend on how he phrased his request. Did he ask whether you felt up to visiting them, given that he is probably bursting with pride at your (joint) baby and that they may indeed appreciate the visit? Was it a more bracing right, you must be ready by now to visit ..... his in-laws...
Who else have you visited already? What else would you be doing in that time? What will the weather be like, what are the chances of you getting stuck unable to travel in bad weather, what might you miss?
Once you have decided between you to do then I am all for letting go any objections and putting on a sunny face. It's how you get to that decision, what factors you take into account, that would matter to me.
It's not that I never do anything i don't immediately want to do, but if DH wants me to do something, I expect to understand why and have the choice to decide what I do. Life is just too short to do things against my will, against my better judgement. Its important to me, as an adult, that I get to chose what I do.
Doing something, with an outwardly cheerful demeanour, that makes you feel a bit crap is not a sustainable way forward. Being honest with your DH and working out together what you will do, is an important skill for any two adults, and becomes essential when you have a baby together. Enjoy!