Elvie Pump help!!

I need help making this pump work for me. It was too expensive not to be able to use! I’m 4 weeks postpartum. Couldn’t breastfeed directly Bc it was so painful and pumping just worked better. According to size instructions I’m 21mm. So I purchased the shields. My nipples are in pain still. I have a pinching feeling while I have them on. Constantly feel like I have to rearrange them to see if that’s the issue. I try to align my nipples to the shields per the instructions. I don’t know what I’m doing wrong!! I’m getting so stressed. Already not making much milk. Just enough to get through a day. I don’t know what to do. I dread pumping sessions Bc of the pain. This was supposed to help me since I stopped latching baby to the boob and now the same thing is happening while pumping. Someone pls help!