How can I improve my comprehension skills?

I'll try not to ramble, but the reason I am posting this question is because I guess I'm in a phase in my life where I feel, in comparison to some of my friends, my knowledge is rather limited. I'm a 22 year old senior in college majoring in Business Management, and for the past 6 months or so I've had all the right intentions to become more knowledgeable and intellectual; I strongly desire to have a mind that is well versed with a wide variety of subjects..I want to be able to argue and debate ideas. I just feel like I don't have a strong opinion on many topics. It can be really discouraging to be around some of my friends and hearing them engaged in some deep topics, throwing out a lot of facts, while I sit there with no say in the conversation, feeling pretty much dumb. So I've been really trying to read up on many subjects, whether it be in a book, magazine, newspaper or online article. The problem is I don't remember much of what I read. Even if I have a pretty good understanding of what I'm reading, while I'm reading it, expressing or maybe summarizing what I read to someone is almost impossible for me. I always think, well, maybe I should be going the extra mile and reading the piece of information 2, 3, or 4 times..or maybe I should stop after each paragraph and see if I can explain to myself (or an imaginary person) what I just read..you know, maybe I don't force myself to think and ponder ideas as much as I should..I mean there's always room to work harder, but I just feel like I'm stuck, and it saddens me with graduation coming up and all. My confidence entering the job market is pretty low because of this lack of ability. A lot of respect is lost for people who seem like they don't know what's going on in the world around them. The thing is I know I'm not dumb..I'm keeping just over a 3.0, but I'll be the first to tell you grades aren't everything. I tend to make a lot of excuses for myself and say things like, "well those kids probably grew up soaking in books since their early childhood," or, "their dad/mom is mom is most likely really smart.." I don't know, I hate to whine, its just been on my mind a lot lately. Any advice would be greatly appreciated, thanks!!