Blisters and Marathon training

Hello,

Please can someone kindly help me.

For some stupid reason, i decided to wash my trainers which has made them shrink! I then tried to go for a run and got a huge blister on each heel. I stopped running yesterday and tried again today and they are agony again this morning!

I am running the marathon on 21st April so would really appreciate some help as to what to do. Do i let them heel or run through the pain? (agh!)

My running is going well, I was up to 16 miles last weekend and planned to do 18 yesterday. Is there other exercise that would help me?

Any advice would be much appreciated.
Thank you