Rear wheel catching down tube

So what was the result? This has been running since February now.

ps, hey get outta here bigmel I'm the only horizontal dropout round here!

Has the derailleur moved? You might have to loosen the cable to check. If it's a carbon bike find the correct torque for tightening the bracket and use a torque wrench.

The wheel could have gone out out-of-round? Most modern frames have vertical drop-outs, so wheel shouldn't move too much in drop outs even with a loose QR.

if your rear wheel is catching your down tube, it's far more than a broken axle. That sounds more like a broken frame.
I guess you meant *seat* tube...;)

I am not certain on this point at all but I think that some road tyres may stretch a tiny bit over time...as I say I'm not really certain but this could be a maybe if everything else is mechanically sound
Also check that the wheel isn't bent or the wheel isn't out of true radially, this will mean the radius of the wheel is larger in some points than other, causing intermittent rubbing. If it is out of true you will need to take it to a bike shop to be rebuilt...or just buy a new wheel.

Could be a broken axle.

The tyre could potentially be damaged and have a strange lump or bulge that will cause it to rub....if this is the case do not ride the tire at all until it is replaced, could be dangerous and split at any point

have you fitted bigger tyres ?

Assuming your bike frame has clearance for the wheel and tyre you have fitted (!) then here is how to do up your quick release properly . . .
Undo the QR lever, then lean over and put your chest on the saddle so that your weight is supported by the bike. This will seat the axle properly in the vertical dropouts. With your weight resting on the bike, do up the QR.
Make sure it requires a stiff push with the palm of your hand to close (it should leave an imprint on your palm for a few moments).
If too easy (or impossible) to close, open the QR and adjust the drive-side nut to change the tension required.
The QR lever should close into the triangle formed by the chain and seat stays on the left hand side to be neat and out of the way.

Don't tell me you have horizontal dropouts . . .

The only time it has happened to me was when my rear quick release was left loose. I rode about 70km in a race and couldn't work out why I couldn't stand up on a climb...