Power Issue

Hello all,
I replaced the battery in my car recently as the car was not getting any power to start. As soon as I changed it it began working again. Its been 3 months now, and its not turning on again. I got a jump and it came back so I drove home. Tried to start it again and I get no power. Is there any way I can fix this? If it gets a jump and works the connections are good right? as long as the car is running after the jump its fine, but as soon as i turn it off the power wont come back on. What should I do?

Thanks