You're not a loser. You're just having performance anxiety. Applying a condom has a way of bringing that on.

Maybe try and proceed to manual stimulation of both you and her before you try intercourse again or stop to put a condom on. Applying a condom breaks the spontaneity, it's true. You're too young for Viagra.

Also if you're young and this is your first time and you're worried about being walked in on, try and find someplace private where you're going to have plenty of time and no interruptions. That won't be easy, but if you can relax and not have to worry about rushing and have plenty of time for foreplay, you'll have a more stable erection.