Penis can't enter virgin girlfriend's vagina.only head enters.the first times there was a little blood and now a drop is noticeable.tried lubrication.

You need lubrication: You need lubrication and relaxation on her part and yours, if you both are not relaxed it may be more difficult and more foreplay oral sex and using fingers in the vagina prier to putting penis in the vagina, .If still unable than she should have a gynecological exam to make sure there is no anatomic abnormalities like vaginal spasm, vaginismus, or tough hymen wich is very rare but possible.

Try harder: If at first you don't succeed.... If she's a virgin it may be more difficult and also painful for her. Use warm water compresses and manipulation with fingers. Also make sure you use contraception and protection against std's. Be gentle, but "firm". A rare woman needs a minor surgical procedure by her gyn to make things easier for everyone.