I'm having a hard time + (verb-ing)

By stating you are having a hard time you are letting someone know you are having difficulty with something.  This could be something physical or mental and something that could be overcome with effort.

Here are some examples:

"I'm having a hard time writing."
"I'm having a hard time understanding you."
"I'm having a hard time answering your question."
"I'm having a hard time downloading songs to my iPod."
"I'm having a hard time agreeing to the terms."

With the addition of an adverb you can express in more detail just how difficult something is for you.

Here are some examples:

"I'm having an extremely hard time trusting you."
"I'm having an extremely hard time with my wife."
"I'm having a very hard time finding a job."
"I'm having a very hard time finding parts for my car."