Let's just start with your current problem. This problem, as with many others, can be caused by a number of things. I'm probably going to have to go the long way around to get to what is most likely a small problem. But that's what we lack since I can't be there to check it myself.
First, check to make sure you've got a clean filter. The next thing I would want to know is if your fan and indoor coil (what's conditioning your air to be cool) are clean. After that I need to know that the fan is running properly, more to the point, moving the air it's supposed to without any motor problems. Again, that's the indoor fan, not the one outside.

You can probably check the fan easily enough. After the system has run for a while, listen for squealing or roaring noises. If you're hearing something, that's a fan motor bearing, so you'll have to have that motor replaced. If you hear nothing, cut the power to everything. Then you should be able to get access inside your furnace by removing one or both service panels (usually two). What is pushing the air is not always easy to see, but if it's dirty, you can tell. Then check the motor itself by feeling it. If it's firecracker hot, you've got a motor problem.

The coil is usually pretty hard to get to. I can tell you from experience though if your filter was really dirty or inside the furnace cabinet and around the fan was dirty you may need to have someone out to clean that coil up.

So here's the short answer. If I was there, I could find out in two minutes if I needed to address the preceding issues before I do this one last thing. But I can tell you a lot of the time, I don't have to. It might just be undercharged. In that case, again, you'll need to call someone out.

I hope I haven't inundated you with information. But all this stuff is what makes AC and refrigeration complicated, and why the government (in most states) require us to be licensed to do the work.

Just remember cleanliness is the best way to maintain your equipment. Change your filter when needed, and wash that condenser coil (the outdoor coil) every once in a while, keeping grass and dirt out of it. And again, always kill your power to your equipment before servicing it. I hope that's of some help to you.