I thought you were supposed to tension the chain on the tight spot.
Typically after an initial few hundred miles bedding in an O-ring chain will need little adjustment during its lifespan, most of what adjustment is needed will be to allow for sprocket/outer roller wear. However, once the O-rings start to fail the links will lose their sealed in lube ‘bath’ & this will result in metal on metal contact between the pin & inside face of the rollers that the sealed in lube previously protected. once this happens as in your case, it’ll start to wear pretty rapidly & result in the need for replacement ASAP before the pin wears too thin to be able to take the stress being placed upon it - ie. snaps!
If I was you I’d be very wary of giving it large before the weekend. :pinch: 
Thanks - i definitely took it easy in to work this morning and will be doing for the rest of the week. At least i will save on fuel!!!
Manufacturers usually recommend 1.5" of play in the chain. However, I find that if I adjust to this amount of play, the chain will quickly slacken to about 2" of play. This occurs on both of my bikes.
What works for me is keeping the chain at about 2" of play and cleaning & lubing it regularly (about every 200 miles). This has given me huge mileage from the chains on both my old Blade and my ZX12R.
I know this might sound like a stupid question but have you been re tightening the adjustor’s properly (assuming its not a single swing arm)? Can you actually see each time you adjust the chain that you are needing to move the adjustment point back to make up the slack?
What I mean is are you 100% that the chain is becoming looser or if there is slight movement in the fixed points on the bike.
Just thinking out loud.
Right questions.
what bike is it. this is important as if its something like a 125, it will have a cheap chain on it which will stretch quickly and continually. (although if you have bought the bike second hand, then the chain could be an unknown quantity)
Does the chain have any tight spots? this can be checked with the wheel off of the ground. check the slack, turn the rear wheel through 180 degrees check again, and continue untill the chain has gone the full way round the sprockets (you can mark a link with tippex or a scratch to keep track.) if there is more than a few mm of difference between the tightest spot and the loosest spot it will probably need replacing along with the sprockets)
the condition of your sprockets DOES NOT always give an indication of your chains condition (again cheap chains can wreck easily without overly wearing the sprockets)
Mileage means nothing. your chains life will depend on
A. the quality of the chain, (i had a customer with a cheap quality 'O’ring chain that lasted 3 months on a GSR600)
B.how well the chain is looked after (regular cleaning/lubing/adjusting)
C.the bike it is being used on, (for example big single and twin cylinder bikes are heavier on chains than 4 cylinders)
D. your riding style. if you use lots of engine braking, on/off throttle use this will wear your chain and sprockets quicker)
also the correct amount of slack varies from bike to bike, so make sure that A. you are reading the slack correctly, and that you are setting it to the measurement specified for YOUR bike
I reckon this is his bike Matt 