You did not mention why you want to pump? Are you getting ready to work outside the home or do you just want milk stored up just in case? Getting ready to go back to work and continue to nurse full time is stressful and that might be part of your problem. First and foremost, relax.
A lot of this advice assumes you are going to be working outside the home, because that is my experience, but even if not, I hope it helps.
You need a good pump. This is absolutely crucial. I used Medela Pump In Style. It got me through 2 years of pumping and it never broke down. Drink lots of water. If you are going to be away from your child, you need to pump every 2-3 hours, never more than 4 hours between pumping. Pump both breasts at once, not one at a time.
Lower your expectations. You won't make as much milk pumping as when you are breastfeeding. The pump is simply not as effective. And it is very difficult to increase production through pumping.
Why do you think you need to pump more? I think you could probably google the average amount per session and get an idea of where you are. I never got more than 4 ounces per breast per pumping session. The average would have to be 2 or 3 ounces per breast. Some people can pump a lot more than this, but I suspect this is about average. If it is a caregiver feeding your baby the expressed milk who says your baby is still hungry, consider what they are comparing it against. They are used to feeding formula fed babies and having a lot of formula left over. You simply have to trust your body that it is making enough for your child. My pediatrician always said that if the child is growing and thriving, you are doing ok.
Breastfeed your baby whenever you can. Very frequently on the weekends. Whenever you are with your child, nurse. Put everything else on the back burner. This will maintain your production and increase it during growth spurts.
And if all else fails, supplementing with formula won't hurt anyone. And it might just lighten your load and give you the relief you need to relax!