I'm 11 and think of sex a lot. Normal or not?
It is very normal for a boy who has passed puberty. It is something that men can avoid. Since our genitals are external and respond to the least provocation, we quickly learn that having an erection and thoughts about sex are connected. Also, as your body begins to produce semen, the seminal vesicles where the semen is produced enlarge. This causes a signal to be sent that men perceive as being a desire for sex. It is really signal that the seminal vesicles are getting full and need to be emptied. The more full the seminal vesicles get, the more demanding the thoughts about sex. It takes a while for the body to get the pattern of when to ejaculate, such as through a wet dream.
Since you are eleven, it might be that you haven't had an ejaculation yet and what you are feeling is the building semen. if this is the case, then sometime very soon you will be having your first ejaculation.
What you have to be careful about is to not let your mind wander into thinking about immoral sex, such as having sex before marriage. It is hard because our society is pushing to make fornication acceptable, but God says it is a sin. Sex only belongs in marriage (Hebrews 13:4). Nor do you want to purposely stir up these sexual feelings by doing things like looking at pictures of poorly clothed women. The feelings are hard enough to manage without putting bad images in your mind. "For this is the will of God, your sanctification: that you should abstain from sexual immorality; that each of you should know how to possess his own vessel in sanctification and honor, not in passion of lust, like the Gentiles who do not know God" (I Thessalonians 4:3-5).