What you describe sonds like you are forming a "puck" or printing at too low a temperature. If its an all metal hotend the nozzle might not be tightened properly and if you have a puck once you will get it over and over until you properly clean and assemble the hotend. You also could have your extruder improperly so it does not push the filament properly. You also could be printing too fast for your setup (filament/temp) and then your heater cartridge or thermistor could be loose and the temp the printer thinks the hotend is on is not the actual temp.