Diabetes, cardiac issues , drugs, infection and increased water intake are the usual culprits for this issue.Since we have ruled out most of the causes with blood and urine investigations we can go to rarer cause.
Gynecological issues should be ruled out like fibroids compressing on the bladder
, cystocele etc.Scans can rule out this.
Another rare cause is Over active Bladder.There is no specific reason to develop this condition.It can appear at any age.
If that is the case then the treatment starts with life style modifications like restriction of water, exercises, weight loss and avoidance of tea, coffee,smoking , alcohol etc.
Kegel's exercises are helpful as it helps you retain more urine in the bladder.
Bio- feedback exercises are also useful to improve the bladder control and can be tried.
If all these measures fail to give benefit, then medications can be tried.There are lot of medications for this condition, some of which are vesicare, detrusitol, trospium and myrbetriq.
Desmopressin spray is a medication which decrease urine production and will take care of this night time frequency.
There are other recent advances like neuro-modulation and botox,but it is reserved for stubborn cases only.
I hope this gives you some options to think about to tackle your problem.