Central air basically will not cool a house much more than 20 degrees less than the outside temperature, no matter what you set it on, particularly if it is a smaller or older system. So if it's 100 outside and your A/C is keeping your how less than 80, it's doing about all it can do. You might as well turn up the thermostat to about 75 or so; it won't make any difference. Turn it down at night so that the house is at its coolest in the morning. This is normal living for us in Texas.

Our A/C compressor pooped out on us a few days ago; we have an old system we need to replace and this is our almost annual compressor replacement. LOL!

Get some fans. Take a couple of cool showers during the day. Do any housework in the early morning and just sit and relax in the afternoon. A cool ice pack (a bag of peas works well) on the neck does wonders if you're miserable.