Heavy Brown discharge - pregnant ?

Ok...
My cycle started on Mar 4th and its usually 5 days long [sometimes I count 6 if it was a little heavier].. Anyway appox.the 21st I started getting a heavy DARK DARK discharge.. No fowl smell -- in fact it smelt and resembled another period. Well today is the 26th and it finally has stopped.. It wasnt as heavy as a usual period but it was enough to really annoy me. Im worried. I dont have any crazy prego symptoms or anything of that nature.. In fact, my period isnt due to begin until roughly the 2nd to the 4th.
Whats going on?! Should I be concerned?
I did have intercourse with my bf prior to this, perhaps the 17th but we are always extremely careful and well protected.. Neither of us have a history of any STDs or HIV or anything of that nature..
I am not on birth control but am strongly considering it.. Right now we rely on a condom and the "withdraw" method.. [at the same time of course].. So even with a condom, and he climaxes, its never internal.
Am I freaking out over nothing?

I also want to add, I did not have any cramping or breast soreness.

I am considering being checked out.. Who do I go to for these tests? A general/family practitioner? Will they be able to run std/hiv/pregnancy tests? As well as do a general exam for my over all health?
If I don't make it soon enough, when is the earliest I can take a home test?
If I get my period normally [the 2nd] am I okay to assume all is well? Or should i still do all those tests ?
Thanks