Headaches/lethargic/thirsty?

ElleWithEndo • 6 IUIs, IVF (chem preg), FET, lap surgery for endo, another failed IVF...and now surprise BFP!⭐️Instagram: ellewithendo
I'm 18 weeks. After breakfast today I felt really lethargic and got a headache and could feel my heart beating a bit stronger (maybe faster too). I also felt thirsty. Breakfast was yogurt and granola and apple slices. Anyone else experience this or know what it could be from?