SUBREDDIT: r/relationships
TITLE: (Advice) I (M21) don't feel like I'm good enough for my (F20) girlfriend. What can I do?
POST: Been in a relationship with my gf for about 5 months. And I've been having issues getting her to orgasm etc etc, the sex is fine but I feel like I'm useless as I'm not exactly hung like a horse, she says "it does the job" to satisfy her but never makes her orgasm from piv sex, but being at best 6 inches I think she's not telling me the whole truth as I know her past and she's had guys with bigger ones than me. Anywho,  is there anything I can do to be a better lover/work what I've got better/tips tricks etc? 

I'm still new to the whole relationship and sex thing as my previous gf was a starfish in bed, and we'll I got nothing out of her really. My new gf is really experienced and I feel like I'm way out of my depth. 

Any feedback positive negative tips whatever will be extremely helpful.
TL;DR: 
need tips/help for my sex life as I feel 6 inches doesn't satisfy her and I don't have much experience.