It's not really a struggle, it's needed suspense of disbelief. How does a dude that can outrun everything, even himself continue to be interesting without ficitionally imposed limits?
By presenting characters that still, even with super speed, cause him to struggle.
Such as Steel, who could only be defeated by Barry understanding his powers more and tapping more into the speed force. Introducing plot induced stupidity is just terrible writing, I wont even waste time explaining why.
Umm that is not what they are doing though. His rogues gallery is catered to counter his speed, the writers write villains that actually has a chance to beat him. Like Cap Cold which can freeze and take away his traction or just freeze the whole room and slow down your metabolism immensely. Mirror Master that can confuse you and teleport faster than he can run. Trickster who just has gadgets that explodes and hidden traps. Zoom who can run as fast 9if not faster than him at times). Grodd who is telepathic and a super genius and can withstand Flash flurry of punches (Flash has no super strength). Weather Wizard who controls weathers.
I mean you obviously have to suspend some disbelief, it's a comic but you really just need a little imagination and it will all work out just fine and still enjoy the show.
Plus in the show, he is a newbie and that is pretty much what the whole season has been, Wells helping him get better, get stronger, get faster. Barry is also a nerd and has no street smarts (and friendzoned) and his fighting skills are lacking (Oliver tried to teach him that and told him to keep training). I mean this is really all you need to know right now, he is just a newb that is still discovering his powers while others here just want him to be an expert in every aspect of his powers from the get go.
But at the end of the day, it is just the typical hero/villain scenario, he encounters a villain and doesn't know what they can do and loses, retreat and figure stuff out and then win. Rinse. Repeat. It really isn't that difficult to understand especially with him just starting out.