Getting frequent urination at night time. What could be causing this?

Hi,
There is a significant possibility you could be having a urinary tract infection if your frequency has gone up suddenly and are indeed passing urine very frequently especially in the nights.
Hope you are not a diabetic.
You should get a urine examination, a urine for culture and sensitivity test done. Hope the streamof urine is not a problem.
Once in a while a ureteric calculus can be coming down the kidneys and can cause strangury where a patient feels the urge to void, but voids small amounts with discomfort. usually this can be excluded by getting an ultrasound examination of kidneys and bladder where an estimate of how much urine is being left inside the bladder after voiding also can be assessed.
You will be able to get good relief with medicines belonging to a class of drugs called anti-cholinergics like Solifenacin, Darifenacin. Sometimes citrate solutions orally might help. Antibiotics obviously need to be given in the presence of active infection.
Hope I have been able to help you.
Regards.