Blot - I don't think it's necessarily the Vagifem causing your problems. You are very anxious about using this so I suspect you are clenching and when the urethra is sore and inflamed (which happens following an infection or as a result of atrophy) then the clenching makes things worse.
We are told to do pelvic floor exercises but we are seldom told to practise completely relaxing our pelvic floor.
I assume you taking showers, not baths, and taking great care not to let anything perfumed( especially shampoo) get anywhere near your intimate area? Are you avoiding caffiene, fruit juices and highly acidic foods?
You also need to try and put your feet up and completely relax your pelvic region for half and hour in the middle of the day if possible.
I also suspect your vaginal flora is out if balance. I do know that Multi Gyn Actigel stings after application but have you tried using a small amount on the end of your finger and pushing this up inside 2-3 times a day and, after inserting the gel, wet some kitchen roll with cold water and hold this to your intimate area, for about a minute, to cool the area and help it to relax?
I know my urethra is very sensitive and will react to any changes in the flora and this will make me burn and want to pee.
I use a whole variety of strategies to keep things comfortable and by using the Vagifem every 3 days with Multi Gyn (occasionally when needed) and Sylk every day, I can control things most of the time. I still get up to pee between 3-4 times at night because that seems to be when my bladder fills up.
Sitting too long, getting very hot around my intimate area, tight trousers and of course sex, all tend to trigger problems.
BUT relaxing and letting the air get to my intimate area really helps.
BTW - do not wear pajama bottoms or pants in bed. DG x