Hi Dipsy and welcome to the forum.
Whenever I am prescribed something new I go home and look up the name of the drug on this website:
http://www.drugs.com/invokana.html
Here you will see info about side effects, interactions and other important things you need to know. You can ask your doctor about anything in there that concerns you.
Which side effects in particular are you nervous about? Have you tried any other meds for your diabetes apart from metformin? Do you know what your latest HbA1c or fasting blood glucose result was?