Is this normal or do I have a certain condition?

I'm 16 and I've always had bad grades since I'm 5, from age 7 to 12, my grades were from 63 to 87 in english. It got worse in middle school in high school( grades from 61 to 83). When I was in kindergarten and also in elementary, I always had trouble counting,reading,drawing and cutting shapes When Lego's were given to me I didn't know what to do with them. It felt like I had no imagination or something. My dad used to give me extra textbooks for my math class in 6th grade because I almost failed. When I try to pay attention in class, it's like the information just doesn't sink in. I listen to the words and I completly forget what my teacher said after five seconds, it's not that I don't understand, the words just get out of my head or something. I had two concussion when I was 5 and 6. I'm premature also, if this helps.