We've been there with Jess as well, 2 blocked bladders and constant cycles cystitis this year, nothing at all medically wrong with him all down to stress.
For us we worked out the stress was us going on holiday and leaving him (despite company every night - my dad sat and watched telly with him) then the Christmas decorations came out and then 2 sets of neighbour's rehomed dogs, and finally Milo arrived, the arrival of Milo has actually helped Jess gain some confidence.
Being at our wits end we tried everything with Jess, (feliway, rescue remedy etc etc) and in the end we paid for a behavioural consultation, and its worked wonders.
Basically Jess does wee, he'd go once or twice in 24 hours, he would fill himself up and hold it till he had to go, so under the advice of the behaviourist we changed the litter we use and given Jess more choice of trays, and closed the door to the utilities cupboard (where they trays are) slightly so he has privacy when going, and the results have been dramatic he is now weeing 3/4 times a day.
But we also give Jess a cystease twice a day and also a Zylkene capsule, the Zylkene helps to relax him and even before the behavioural stuff his body language changed lots he was a lot happier. Jess also had urinary food, mainly because it gets fluids into him, his not a drinker and never has been. We have a water fountain and occasionally he will play with it. In the warm weahter I've been giving him tuna smothered in water to keep the fluids going into him.
Anyway this is my story of a stressed and nervous cat, I hope some of it can help you