What flow nipples are you using? I have used the Playtex nurser's all along, and LOVE them!
How old is your lo? That might make a big difference in the flow of nipple you are using.
My first suggestion would be to just buy the next flow, and see how that goes.
Also, the liners for the Nurser's now are "self standing" although they still make the old kind - I could never figure those out! We get the self standing ones (pre-formed) and I LOVE them!!
Let me know what else I can do to help!