Lump I need advice

I found a lump back in October 2020 I went to the doctors in February 2021 they felt the lump aswell they refered me to the breast clinic I got seen and the doctors there couldn't find the lump and it wasn't shown on the ultra sound but I can still feel the lump I don't no if to go back to doctors or not don't want to waste there time if there's nothing there but I can still feel it