cramping which is very unusual, light pink discharge?

I have been experiencing very strange hormonal problems for the past few weeks. I got my period on time as normal this cycle, however it was only 2-3 days instead of my usual 4. After my period ended I started feeling really tired and run down, very similar to the feeling when you have a cold when your whole body just feels tired and worn out. I broke down and started crying for hours for no apparant reason. I have had cramping which is very unusual for me after my period. And about 5 or 6 days after my period stopped I had very light pink discharge in my underwear and when I wiped, this only happened once and was accompanied by light cramping. This has never happened to me before, and I usually have a very regular cycle. I am thinking that I may be pregnant and that maybe the spotting was implantation bleeding? But I don't know how that could be since it was less than a week after my period. What could be causing these symptoms?