white grains in Urine?

Ok so I havent got this in a while but I want to know what it is just in case it comes back. When I went to the toilet the urine would come out normaly and then at the end it would kinda struggle to get out and I would have to force it a little, then I would get a kind of stinging sensation and a burning sensation in the anus region, then at the tip of my Penis there would be alot of little tiny white sand grain like things that are pretty hard... like sand grains basically. Im 18 and I want to know what the hell it is coz it scared the heck out of me... and its happened many times before. Also I am very healthy and fit so it makes no sense. Tweet