I'd just say make sure you are eating enough calories wise as fruits and veggies are much less calories than meats and cheeses
Also it may just be your body adjusting and "de toxing" from pre plant based foods... Say if you ate a certain food quite a bit like cheese - this can trigger headaches because of what's in cheeses for example
I had similar although some people don't experience a change that they notice
On a side note - when I stopped drinking coffee I had 3 weeks of horrible headaches
then nothing... This is why it could be your body just adjusting and giving you a signal that what it's used to may not be there anymore
Or it could just be you need to eat a bit more
hope they stop soon xx
Just to add.. If you are now eating soy products regulalry and didn't previously this could also be a factor