Why has my ride changed? The bike is a Specialized Camber 29, about five months old, from a shop about 220km away.  

Something feels different in my ride, and I'm wondering what it is.


the rear goes sideways in sand much more often,
there's an different running sound from the rear tyre, at a different pitch than before,
the rear tyre is about 3mm taller than the front tyre, measured with callipers from the inside of the rim to the valleys in the tread,


After a flat rear tyre last Thursday, I took the wheel to a local bike shop 70km away, who took the initiative to insert the old tube as a covering for a new tube.  There was already a protective layer of some sort between the tube and the tyre.  The region is known for thorns, but there was no evidence that a thorn caused the flat.  I put the wheel back in.  I'm wary of blaming this event, because I don't have enough experience.

I ride twice daily for half an hour each time, on dirt roads, for about 6km.  

I lack the tools and strength of hands to repair the wheel myself, and have no other riders nearby.

There's a possibility that my failure to maintain the suspension system may have caused the problem; but I don't know enough about it to tell.  It has been left alone for the life of the bike.

There's a possibility that recent light rain may have changed the sand.

The rotation markers on the tyre are pointing in the right direction.
The protective layer is known as "rim tape". The old tube shouldn't remain within the tire - the only thing inside the rim should be the rim tape and the new tube. 

You may have different tire pressures than before - have you tried playing with them?