do i have a small penis?

i can never give my wife an orgasm from missionary or doggie positions....only when she sits on top of me and she grinds on me back and forth not in and out or up and down....she grinds and squeezes her muscles around her pussy and aftre like 2 minutes of that while I am sucking on her breasts and nipples she comes really hard and is basically done with me...

My dick is 5 inches fully erect...is this why this is the only way she can come from me? is 5 inces small? Do you think if she had a 7 to 9 inch cock in her she could come in any position? Would she really have a lot more pleasure and possibly be multi - orgasmic?

Thank you for your responses

Face it! Five inches ain't big but it'll get the job done in a pinch. My advice is to be okay with her getting something bigger on occasion. If you were her, you would, wouldn't ya?