Puncture woes

 I biked to work yesterday.  I left at 6.15 and was at my desk before 7.30 which is not bad considering I have to shower and change when I get there.  I had hoped to leave a bit early to avoid traffic on the way back but I couldn't get away until 4.15.  I had only got about 100m before I realised my back tire was flat.  Lots of fun replacing the tube in 35C heat.  That fixed I had a dfecent ride for a while although it was hot and the traffic was quite heavy.  Then as I got to Bloor and Sherbourne I realised something was not right.  Sure enough the tire had gone again and, of course, I'd used my spare tube.  It's a forty minute or so walk home from there so I did.  I got in at 6.35.  I guess I need to figure out what is going on.  I think there must be something stuck in the back tire but I haven't had time to look yet.  Besides I have a new bike coming which I expect to take delivery of Thursday or Friday.