I am 18 years of age. I tried keeping my virginity -- until three days ago when I lost it to carelessness. I feel very bad right now. I have offended the Lord, and ever since I have been praying. I need your help and prayer. Will God still accept me back as His son? Please reply.
God doesn't keep anyone from returning from sin. He only requires to things from you:
Repentance: Which means changing your mind about your sin and changing your behavior. "Now I rejoice, not that you were made sorry, but that your sorrow led to repentance. For you were made sorry in a godly manner, that you might suffer loss from us in nothing. For godly sorrow produces repentance leading to salvation, not to be regretted; but the sorrow of the world produces death. For observe this very thing, that you sorrowed in a godly manner: What diligence it produced in you, what clearing of yourselves, what indignation, what fear, what vehement desire, what zeal, what vindication! In all things you proved yourselves to be clear in this matter" (II Corinthians 7:9-11).
I suspect that it was more than just carelessness that lead to your having sex. I suspect that you didn't admit the power your sex drive has over your behavior. Whatever the cause, you need to recognize what caused you to drop your pants so that you can avoid similar situations in the future. You want to get to the point that people who know you in the future would never think of you being in the type of guy who would take advantage of a girl.
Confession: You can't really change unless you admit you have a problem. Thus, God requires that you admit your sins to Him. "If we confess our sins, He is faithful and just to forgive us our sins and to cleanse us from all unrighteousness" (I John 1:9).
The question has never been will God accept you back. The question is are you going back to God?