Feeling sick 36 weeks

Posted this earlier but got zero response, figured I'd try one more time now that it's a little more popular time of day... So for the past two days by midday at work I feel sick. Headache, stomachache, exhausted. I left work early yesterday and went straight to bed. Have to stick it out today but I'll probably be straight to bed again. I'm 36 weeks tomorrow and also have an appt tomorrow so I will definitely mention it to my doc. Just curious, anyone else experience this? Any explanation or recommendations on how to avoid this?