It's a funny time to get a new batch of feeling crap. You're right in the bit where you should be feeling ok so I'd get checked, I started having funny turns about this point and turned out I was getting low blood pressure from anaemia, easily sorted so best to get checked. Call in sick if you want, you are pregnant! x
I'd say low iron, I had that about 25w and I remember being elated when the blood tests they did at 26w(? around then anyway) came back with low iron, because it meant I wasn't going to feel like that for the rest of the pregnancy.
I'd call and ask to see a midwife or GP tomorrow. I don't think it sounds awful, but definitely something to get checked, especially with the headache. Pregnancy is not a time to soldier on, always best to get things checked.
Call in sick tomorrow, surely your employer would rather you missed a 'fun' day than an actual work day?
I felt much more tired during the 20's weeks and often went to work late, and spent most evenings laying on the sofa dozing. Have a rest and take it easy tomorrow and if you still feel rough see your gp for reassurance. I'm sure you ate fine though, just tired!
I started feeling like this at about 25 weeks and have just assumed its a return of the tiredness and symptoms from the early stages, thought that was what happened? Maybe will start taking my vitamin again if its not normal.
The blood pressure thing is really hard to find out about, I have always suffered with dips in blood pressure (even when not pregnant) and obviously by the time you get checked it's normal again! It's something I just figured out for myself over the years. Good idea having bloods taken. Don't worry about the baby, babies are parasitic so will take everything it needs from you leaving you to suffer, sounds horrible but you'd rather that than the other way around. Good luck and I hope they find out what the problem is. Try to get work to ease up on you too! x