Wtf is with my back

[Jokerlsk]

Guys, i'm not completely out of shape, but i'm not really where i would like to be..... I want to start working out with my dad (who is a beast) but he told me he won't take me to the gym w/ him until i prove i can do 50 consecutive pushups (he's old school...) Anyways i'm doing that plan on hundredpushups.com and i could do 13 w.o stopping but my back kind of hurts when i do one. Is this because i never really do pushups? Or is it because i have some sort back problem? Will it go away if i continue the plan? Or will it worsen? I would really enjoy your feedback

 

[KontrollerX]

Are you in good shape otherwise?

Do you do cardio and any weight lifting at all??

 

[Jokerlsk]

Yeah, i am.
I'm not overweight but i'm def. not underweight
I'm 6'2 180lbs and i lift sometimes

 

[eldafar]

Are you doing them with good form? You're not letting your lower back drop, are you? That's the only thing I can think off the top of my head that could cause back pain.