Seeing that my wife is pregnant and only in week 9 at the moment I actually don't understand how anyone can be a decent adventurer while being in the first three months.
Outwards it does not alter much, she lost a few pounds but is now gaining a few pounds the big thing though is the not visible, nauseau, constant nauseau that lightens up a bit if she eats something, a piece of fruit or so is enough for a few hours. Couple that with complete fatigueu after going shopping. This is walking to the grocery store, picking everything and for her just walking back (I'm the mule). After a full days of work cause she still works she falls asleep on the couch.
IF you're even unlucky like my wife then you can add another thing to that and that's stomach cramps, in a way us men can't comprehend, which our gynaecologist said is normal due to not seeing anything wrong with the pregnancy. It's her womb expanding. Most women only have this a few days or so. Still she got ordered two weeks of bed rest cause this pain could really cripple her and make her unable to do her work. (She attends and helps senior citizens in a nursing home).
But then again, our gynaecologist also said that pregnancies differ from woman to woman.