Weird period

So i was 7days late i took a hpt on the 15th,17th,and 19th. All were negative the one i took on the 17th had a very faint second line. What i thought was my period showed up on the 17th but its very lite most of the time its just spotting. I changed my diet 2weeks ago so i thought thats why i was late but i've never experienced a period this late and lite. I know i need to make a doctors appointment but does anyone know what could be going on? Thanks in advance. ☺