Your IQ is not fixed! You can improve your intelligence.
Imagine waking up in the morning and first thing, you are given a test. How will you perform? Not good. You need to get up, move around, have something to eat, but what you eat is important too, then your body digests the food, giving you energy. You go out and exercise, getting your blood flowing to your brain and supplying it with calories, energy. Now take the test. You will do much better.
Exercise, eat right, and try to process information in bits and pieces. Sometimes looking at it all at once is overwhelming and confusing. Baby steps. Read a paragraph, stop and think about what you read. Write about what you read, summarizing it. That way you aren't just reading words and not comprehending. After a while you will process info better. Actually writing out your thoughts will lead to better communication. Stop wasting time with video games and things that just won't benefit you in a long run, even TV.
I have to tell a story about a woman who had two young children in school and they were doing terribly, they always came home with bad grades. But all they would do is come home and watch TV! The mother got rid of the TV and told them they had to read a book and write a report and give it to her. She couldn't read herself (but they didn't know that). She would look at the report, shake her head in affirmation, "That's good, keep it up, you can do better." She gave the kids positive encouragement. They figured out the rest for themselves by reading, improving and learning. Twenty years later, they both became doctors! There used to be a commercial on TV: "Be all you can be, read." Don't ever think that you are not smart and therefore will never accomplish much! You can. You may not be a rocket scientist, but you will succeed if you keep at whatever you find interests you. God gave us all talents and abilities, we just need to find them. You are good at something, discover your strengths and find what interests you and that will be your path.
There are certain brain nutrients that enhance mental abilities. Natural Vitamin E, Huperzine A, Vinpocetine , etc. You can get those at a Vitamin shop. Certain foods like fish are consider brain foods, that contain neurotransmitters used in the brain like choline.
Basically, the wrong foods can make you have brain fog. These foods like sugar, fined flour, donuts, junk food, processed food that contains high fructose corn syrup, hydrogenated oils, etc., can lead not only to obesity, but poor mental functions as well.
Healthy body, healthy mind. If you aren't exercising and eating right, you will not perform anything at 100%. God made people with brilliant minds, average and below average. We need to accept this and just do the best with what He gave us.
Here are a few cites that may help.
Fourteen Ways to Increase Your IQ - Daring to Live Fully
15 Brain Foods To Boost Focus and Memory - Dr. Axe