I had my bitch neutered on Friday. She seemed ok on Friday but rapidly has gone downhill. She is not urinating and keeps going round the floor in circles sniffing it. I took her back to the emergency vet this afternoon and he gave her a shot said her anal glands may be full and that she may have an infection.

She came home and was really quiet. She is eating small amounts, drinking and passing motions , she has only just had her first wee now. I have spken to the vet again this evening he said that I should have no reason to worry too much as she should be OK. This is not my usual vet as it is bank holiday

Help urgently needed!!!

If that was the first wee she had then hopefully she will continue urinating ok. Slowness to urinate  can be a post op problem and having an over full bladder would have made her uncomfortable enough to look unwell. Does she have a temperature? Normal is 101.5, I would definately take her temp twice a day and if it is 102 or higher ring the vet and tell them as it would indicate an  infection.
Most post op dogs are sent home with A/Biotic tablets  to be given for a week or so, did yours have some? What was the shot she had - do you know? If the vet thinks there may be an infection she should have a course of anti biotics imo.
Full anal glands may make her a little uncomfy but wouldn't normally be responsible for actual illness, unless the gland/s are infected. If they were full, I wonder why he didn't empty them? It only takes a moment.