One day period, very light

This sounds similar to what I went through in June. My period was a week late and well it was about 4pm when I felt a leak and when I went to the bathroom noticed very little red. 

I figured I started so I put in a tampon. Well about 9pm I took it out and hardly anything was on it except light brown blood(guessing it was old blood idk).

I even had sex and no bleeding occured. 2 days later when I went to wipe I had the same brown blood(?) but only that one time. 

Starting to wonder if it was really a period or just spotting because the one before that was the average length for me, 4 days, but started the same and stayed really light. 

I wish I could give you an answer but I don't know. I'm going to the doctor soon though.

 

Some say cycles can change for no reason but I just don't think that's the case for me. Right now for July I'm 2 weeks late just like the one before June. 

Only answers I get is things like cysts or fibroids but looking up other symptoms for those, I really don't fit them. 

I did not miss my period at first, but this time I had a period only for one day. Actually, the first day it was light and the second day it was very light. So I wanna ask what does it indicate?