There is such a thing as an implantaion bleed which results in spotting but the best thing for you to do is to call your local hospital and speak to someone in the 'early pregnancy unit'. They will ask you a few questions and then decide if you need to go in for an early scan.
Generally they say spotting is normal in the 1st trimester, unless you are also in pain, but it is a good idea to call the EPU at your hospital to put your mind at rest. I am experiencing the same thing with a little pain, so I am having a scan tommorow to check everything is OK. It is a little scary but the doctors say they think it should be fine, and the fact I am dealing with it is really helping me to relax.
(in fact i am quite happy that I amgetting a scan before 12 weeks!!)
I have answered your question re exercise in family, but reading this, i would suggest no exercise until you have seen someone about the spotting
good luck