Brown discharge almost a week before period

This is my first post here, and one that I hope someone can respond to in attempt to put my mind at ease. First here's some background info to help possibly determine the source of the issue I'm experiencing. I'm in my late 20s and I'm NOT sexually active now. I just had to get that out of the way, because STDs and/or pregnancy are not a possibility here right now, but the question is about my period.

I have always had very regular periods from the moment I began my menstural cycle at 14. My periods always begin at the very end of each month or within the first 5-6 days of the following month. So, you could say they vary slightly but always occur regularly between the 29th-6th of the following month. Something seems to very "off" this period for the first time ever, and here's the problem. This passed Sat. (the 28th) I had quite a  bit of brown discharge instead of my period beginning. It may have been tinged with blood, but if it was than it was too light to be noticeable. The brown discharge continued very slightly until Monday (30th) in the evening. Monday evening blood began right before I took a bath in attempt wind down that night. when it began it was considerably lighter than usual (I tend to begin very heavy and cramp within the first 2-3 hrs). Thinking nothing of it, because it was relatively on schedule as usual, I went ahead with the bath just grateful not to begin with intense cramps that usually occur.  

 Here's where everything gets odd and what has been concerning me. By the time I got out of the bath that night, my period (or what I thought was my period?) had completely stopped. Now, I know it  is perfectly normal for a period to take a "pause" during bathing and right after. It has always been that way for me, but has returned full force (esp on the first day) minutes after bathing. However, very strangely this time it never returned after the bath -- blood, any discharge, all signs of period ended that same night I believed it began. It's now the 2nd of the month so it wouldn't be "late" if I started in the next few days instead, but question is, was the brown discharge followed by very light bleeding on Monday just implantation bleeding and not yet the start of my full on period which (hopefully) is yet to come? or was this a very short irregular period that I should be alarmed about? My periods usually last 5-6 days with heavy bleeding during the first 2 days. They never come and go this fast, and they almost always give me cramps the first day. I haven't had the slightest sign of pain or any other signs/symptoms that a normal period is still on the way. 

My friend wants me to see a doctor right away, but I want to keep a "diary" of sorts to see what happens for a while before running to the doctor. Right now I'm not even sure whether to consider this a skipped period or if my cycle is just changing schedule a bit. Has anyone experienced something like this once before at a time when they haven't been sexually active? If so, did your period return to your "normal" the following month or two? Once it did return, what was the main factor you believe got things back in the right direction?

I know stress can affect your period, but can it cause a scenario like the one I've described? I'll admit that I have been under a lot of stress lately concerning a leg surgery I have coming up, but I've dealt with that before, and I wouldn't think that kind of stress would cause something like this. I've also had a bad cold/sinus infection that began (coincidentely or maybe not so coincidently?) right when the brown discharge/short period came along. I have a doctor's prescription for the sinus infection/cold, but wouldn't think that would change my period either. I didn't start the prescription until today either so the odd period ended (or appears to have ended?) before prescription began.

So, considering all these factors, has anyone experienced something similar to this before and returned to their usual cycle? Do you believe I need immediate medical attention at this point? Should I consider this a missed period, one that was extremely short, or IB that will lead to a period as it is still the beginning of the month? If you read through this entire rambling post, I really appreciate it  and any help or insight would also be greatly appreciated. Thanks in advance!