Hi
I am very new to this and don't want to look like I know all about it, but lots of your symptoms do point to a potential pregnancy.
It is probably a good time to start thinking of buying a pregnancy test about now.
I did a test on the day my period was supposed to be due because I had been getting lots of the symptoms that I had read about such as a bit of brown spotting, mild nausea, sore nipples and abdominal and back cramp, and the test came back with a very bright bold pregnant sign much quicker than it said on the pack.
Having said this, periods can bring a lot of similar symptoms so you may be worrying for nothing.
For a definite answer I recommend the digital clearblue test that gives you an answer in letters rather than a blue line, which must drive people mad with doubt.
I would find out as soon as possible, so that you know where you are going from here.
Let us know how you get on. We are all here for you. i only joined the site yesterday and already I feel really supported.
Best of luck