here your back pain can be related with either the muscular weakness for your back muscles or else there will be a problem with lumbar disc. for this to get evaluated you need to consult a orthopaedic doctor who will suggest the needful. now the next problem is frequent urination here it can be related to diabetes but you need to do confirmation with your sugar test as well hba1c test. for frequent cramps in your muscles there might be a possibility of vitamin b deficiency so i suggest to take test on vitamin b deficiency and also Keep vitamin b rich diet in your food. you can also take vitamin b tablet as a supplement. as a physiotherapist i also suggest to do back strengthening exercises as per the suggestion of your physio and do take physiotherapy treatment which can help you to relax your soft tissues as per your physiotherapist guideline. along with frequent urination, muscle cramp if you also have pain in abdomen Then i suggest to do ultrasound for your abdomen and based on report do the needful by visiting your physician. you can also use hot pack for your back this will help to reduce pain by having relaxing and soothing effect on your soft tissues. take care