Can you really be forgetful when I haven't had a decent nights sleep in over 2 weeks how dose it affect you?

Absolutely. Lack of sleep is one of those things that can make us forgetful and not retain memories as well. That's why they say to get a good night sleep before a test - it helps consolidate memories and facts. If you haven't slept well in 2 weeks, you will feel tired, sluggish, and not as quick mentally.