So I've definitely been over doing it on the bike and my back has been discouragingly painfull the last 5 days. So, thanks to attackpoint I wrote down my activities for the last 6 weeks and could analyze where things went wrong. Had a meeting with my chiropractor and booked an appointment with the doctor to discuss progress and POA (plan of action).
mountain bike (errands) 15:00 
#2 on a more positive note: I have stuck to my goal of not using my car for errands, for an entire week now. Not that difficult once you get used to thinking this way. :)