So many things!
That 'morning' sickness isn't reserved for mornings, nor for the first trimester! And that even with cyclizine stopping the actual vomiting, you can still have constant nausea.
The horrendous constipation, despite guzzling gallons of prune juice.
Round ligament pain. And pain when, sneezing, coughing, moving in slightly the wrong direction...
The fact that, because everything softens up, if you turn your ankle you will really damage it. And then inevitably tweak it again when there's snow in March...
That, if you don't have an obvious bump, people will continuously ask stupid questions about whether you're sure your dates are right.
The frustration of not being able to keep up with your pre-pregnancy self at work. This last one has probably been the worst for me, because I'm usually very tough on myself, and I feel like an abject failure
Fortunately, all my colleagues are amazing, and the pressure is all from me, not from them at all!