How many times do you actually urinate over the course of a day? How many times do you get up during the night to use the bathroom?
Sometimes, we don't always get our bladder empty when we pee, even though we think we do... if you were getting completely empty, you wouldn't be able to force more out. Not getting empty is called urinary retention and depending on how much you're retaining, it could cause you to start having UTI's and/or other issues. If it doesn't stop, you should talk to your doctor or urologist.
When you finish urinating and feel like you have to go some more, have you tried just sitting quietly on the toilet for a few minutes and see if the feeling subsides or if you'll be able to go again, normally, rather than doing the pushing and trying to force yourself to go more? Sometimes, you might "dribble" 2-3 more times before you feel like you're completely finished.
The other option is when you get finished peeing, simply get up and go about your business and come back later and pee again when more urine has collected in your bladder and you can go without straining. Once you leave the bathroom the feeling of having to pee may go away or you may feel like you have to pee the whole time until you decide to go back and try again...
Heavy straining, like you describe, is not good and over time could actually make things worse.