New mom, sore nipples…

Hi, I’m a first time mom,m of a 1 and a half month old baby girl, and have been breast feeding almost since the day she was born (had latching trouble at the beginning and unfortunately had to feed formula) but was pumping since day one, never felt any pain till I was finally able to get her to latch when she was about a week or old, I experienced the soreness and a little bit of bleeding the first week or so and was suing the lanolin nipple cream which helped tremendously and eventually the pain went away as well as the bleeding, thank goodness but now there seems to be a similar feeling of pain I’m having? Like I mentioned I have been breastfeeding for a month or so now and am having pain in just one of my nipples? I’ve read that some babies can have a preference to one breast or the other, and the breast that is her favorite is really hurting and tender and can be quite painful and the cream doesn’t seem to help like it did before. Are there any suggestions anyone has I would really appreciate it. My older sister had said I just have to push through and just kinda deal with it, is she correct? Will it get better on its own? Please help!?!