Pap smear “not enough cells” issue?

I have had three pap smears in the last year and a half, and am scheduled for another this week. The first three came back insufficient “not enough cell”. But the HPV result was negative. I am leaning toward canceling this coming appointment. I was told by my gyn that if the HPV results come back negative that I would not need another pap smear, than received a call that day saying that I would need another. I also can’t get any answers on why I would continuously get such results. BTW each smear was done by different gyns and were informed of the previous results.
My questions are… Is this a common problem? To keep getting ” not enough cells”? I really do not want to get a pap smear every four months.
Thanks

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