I can relate to this subject. Sorry if this becomes a long post, I can talk about this for hours, lol.

Maybe, your situation is different than mine, it sounds like you just need to learn more on the basics and gain some practice. My issue was that even if I knew what I was doing, my mind would blank out or anxiety would kick in. Driving is one of my biggest phobias at the moment. I hate that this became a problem for me. My parents never taught me how to drive and never cared to because they were overprotective. I didn't even expect that this would be an issue until the age of 21 when my boyfriend taught me how to drive and I started getting panic attacks, just by the thought of driving so I would avoid it. I managed to get my license at the age of 22. Over the time I've gotten better and the one and only thing that helped was actually being behind the wheel on the road and placing myself out there.

I'm 25 now but even then and till this day, I drive to near by places, if I'm being pushed to, or when I feel comfortable. I proved to myself that I can drive, but I still at times there's still that anxiety. I am still struggling but I have someone who pushes me often to go for it and the more I do it the better, so practicing often is definitely the key.

Read driving manuals, watch videos online about driving, this may also help. I also started driving with small cars, but now I drive an suv and I admit I feel sooo much safer!

I would suggest finding someone who can dedicate some time to teach you more often, perhaps even finding another instructor if possible, if not find what you feel will help you improve and ask your current instructor if he can take that into consideration when it comes to teaching.