Lets see what we have here, you are 20 (earlier said 21), and in a relationship for 3 years, have started se recently. You asked, how to make an excitement sex.
From your question content you are asking for tips on making sex fulling of excitement, from your title you are talking about boring. Now which one to take, honestly, I dont know.
Either you have started having sex and feel its boring, nothing like how you heard before. So looking for excitement. Or you are looking for great tips of great sex. I have problem with both the instances. First is, sexual pleasure is kind of a curve, it keeps growing higher due to change of time, add new things, position, experiment etc, it only gets better. After certain time, the upward curve gets flat, on that time one need to add some new idea or think out of the box to get the curve higher again. You have started and already got bored, man, you need to spend more time on this site or other sites if required to learn about physiology, pleasure point, reasoning behind acts, etc. On second part, if you want a checklist of pleasure tricks, hell, we all are doing here in this site. There is no sure shot trick here, how we discuss issues, learn from there and apply based on two consenting adults spirit. If this was a checklist, we would have not so many members, so many question and replies, it would be a Newton's three principle, just accept and execute.
Stay with us, and read for your own need. As I missed my comment before on the upward curve, usual time is around 7 years for getting in the saturation point before it gets bored. You are already bored, thats a severe concern, means you are no longer keen on her, the land is won, its the property now explore new lands.
Finally, you are pretty young, take care of health and consequence, use condom without a fail. Dont try for safe days danger days rule, we know how to act on those, you are too new to know the rhythm.