Frequent urination's main cause in your age group is urinary tract infection and also to rule out bladder outlet obstruction.
1st u have to rule out urinary infection and then consult surgeon to rule out outlet obstruction ( stricture urethra etc)
For Penis size there are few therapies available which sexologist can guide you.
Next Steps
Test: Urine ( routine and microscopic)
Surgeon opinion.
Health Tips
Consult online or visit personally for penile size related query.