Left lower back (between spine & side) squishy lump, nonpianful, moveable, about grape size. what could it be? should i worry?

Lipoma? : If you have a non tender (non-painful), mobile(squishy) and small("grape-sized" or <2 cm?) lump on your back, it is most likely benign and probably a lipoma. Lipomas are a collection of fat cells, and usually not worrisome. If you notice that it is growing in size, becomes painful, or simply feels different to you, then you should see a general surgeon to evaluate and possibly remove it.