It's really just about practice, writing in high school is difficult because you are just learning how to really do it correctly. By the time I finished college I could write 3-5 page papers with minimal effort. If I tried to write one today it would probably be extremely difficult since I haven't done it in a while.

Once you understand the formula it gets really easy. Introduction should have 1 sentence about the general topic, 1-2 about your overall thesis/point, 1 sentence for each of 3-5 points you want to make. Each point should get it's own paragraph with 1 sentence to state the point, 1-2 sentences the reference the source material to support it, 1-2 external references if required, and 1 sentence to restate the point you made. The conclusion should have 1 sentence per point you made and 1-2 sentences that restate your overall point of the paper.