What Causes The Urinary Bladder Not To Get Fully Empty?

My name is Lindsey. I m 21 going on 22 years old and weigh abou 230 lbs. at 5 ft. tall. I had kidney reflux as a child and so did my sister, and cousin. I have a family history of kidney problems. My aunt has kidney disease, my grandma just had a non cancerous tumor removed from her bladder and my mother found that she has blood in her urine. My question is that some days I have to urinate very frequently, but most days its just normal. I have noticed for a while that after I urinate and empty my bladder I feel like my bladder is empty and i m done urinating, however I can sit right back down on the toilet after being done or a minute later and have a few more drops of urine that I need to get out. There has also been a few times when I go to urinate and have to go very badly that I will sit down to urinate and its like there is a hesitation to at first like it won t come out for a second or two then it finally will. I will also add that I never have burning when urinating. I also have pitted edema on both of my lower legs its just a little worse on one side than the other, but it s not in my feet or ankles. So is this all normal or should I see a urologist?