yes that is understandable, that will get better, your arm should probably strengthen, my guess is you may be trying to hard not to sway, keep in mind the car wheels are tied together and you need to let the car do the driving, keep a relaxed but firm grip on the wheel, If you are always tensed up, your arm gets tired quickly learn to relax be aware of the direction the car is going, focus both right in front wher the car in front of you is and also down the road in a straight line or the direction of travel, looking both short and long distance should help keep the car straight, and relaxing tensed muscles will also become less tired over time. Its not easy being a good driver, so hang in there, always give yourself more room than necessary from the car in front, a majority if young drivers? they rearend another car (because they were too close) There is no law that says you have to ride right close to the car in front, back off the gas, heavy traffic is different, Im referring to light traffic.
And something I taught my self to do many many years ago is be prepared to stop the car at any time, no matter what. If could be anything, from a plastic trash can, to a complete spare tire with rim, if your not paying attention, and hit it, it will screw up your car. I have seen thousands of things in traffic lanes, you wont believe it, everything from about 10 tons of two by fours ( the two cars in front of me, slammed on thier brakes at the exact same time, one then shot to the left, the other shot to the right, I said WOW THAT WAS COOL as I went through a blinding cloud of rubber smoke, And HIT A STACK OF LUMBER, THAT WAS ABOUT 5 FEET HIGH, BUT WHEN IT HIT THE FREEWAY, IT WAS LIKE A CAR RAMP FOR ME. I had bought a brand new dodge power wagon, 3/4 ton long bed 4x4 FIVE MINUTES BEFORE, THIS WAS MY FIRST TIME ON THE FREEWAY IN IT, well long story short, it went right over the pile perfect, AMID A EXPLOSION IF SPLINTERS IN A HUGE CLOUD. SOUNDED like I ran over about 400,000 pencils did not hurt the pickup so off I went. My point is, you never know what is on the road, pay attention and if something happens always get off the gas and hold your foot over the brake pedal, just in case. Thats simple, get off the gas, if something does not look right in front of you, and put your foot lightly on the brake, and be ready.