My 2 mth old son has a pinkish red spot in his diaper what is the cause of that? what is it coming from?

well lately he had been spitting up and being very cranky,so i took I upon myself to change his formula and it worked he's having less gas and fewer spit ups now i recently started to see what looks like blood in my son diaper i wanted to know if it should of alarm or should i just wait to talk to his doctor?