struggles with going more than once

so my gf and i have been together for about a month and i have a really hard time (no pun intended) getting it up again at all for a few hours after we have sex. on top of that i dont last very long 3-5 mins most times.

after 4-5 hours i can go again but its 50-50 on if i will be able to finish or if after 10 or so minutes ill just go limp again.

any tips??