A couple of weeks ago I cut my big toenail rather clumsily, and then wore shoes that were a bit tight on a walk that involved going downhill. The next day the toe was quite sore, and over then next three days it got redder and redder, and sorer and sorer. Finally it developed a blister full of white gunk behind the nail (pic).
I went to a chiropodist and she lanced the blister, and some thin and runny pus came out. It continued to leak clear fluid for the next few hours. The chiropodist gave me some sachets of stuff to dissolve in water and immerse the toe in that for 10 minutes twice a day, and that worked really well, although it did make my skin go yellow and dry and flaky for a bit. Together with some antibacterial cream for the night it cleared everything up in 3-4 days. I have been instructed to get proper toenail clippers and stop using nail scissors!