JerzeesLadies' Jersey Polo with SpotShield

I am 5"0', 135, 36.5bust & a 30 waist line i am usually a size medium in shirts, but up above, it says i should get an xl. which one should i get?

Do they run big?

I am 5"2 and weigh around 145. I'm usually a medium so why size should I get?

Does this shirt have slits on bottom lateral sides?