First off Congrats! I'm 14wks too! (this is my 4th though) This is pretty common and not something to worry about if your blood work is fine it just means your body is sensitive!
It could be from heat. I faint every time there are too many people around me - their body heat makes my body temp rise and I faint ---- I now know when I get that clammy feeling that I need to coool down immediately! It also happens if I stay in the sun too long or if I go from extreme cold to heat - like going from a mall to the FL sun ;)
Don't worry fainting is something that we don't really consider normal anymore but it is truly a natural part of our rapidly changing body. Our heart has to work twice as hard and we produce more blood during pregnancy than any other time! And now, especially that the baby has it's foundations laid, it's working on expanding ;) So we're tired faint easily, get huge headaches, tweeks and stabbing pains as the tendons stretch and our muscles separate to accommodate the new life!
Try deep slow breathing - envision your lungs and heart only. your lungs fill with air steadily and completely and release the air smoothly, slowly. Your heart beats a steady thump thump thump, timing the rhythm of your breath.
close your eyes and try to visualize that. it helps alot. well at least for me ;)