Irregular period

So my periods are usually really regular, once in a while they’re late but other than that everything else is usually the same. This time, I got my period on time but it was extremely light and very dark like a brown color. It was like this for two days and now it’s some brown and some normal red color. I’m on birth control but I missed a day and took the next one late. Any ideas on why my period could be like this? Is it normal? Should I go to the doctors?