My front door lock is too loose
From the sounds of it I would suggest that it is time to replace the front door lock. Be aware that there is a huge range of quality in door locks and door knob units. The lowest quality ones are often what is found on mass built homes, condos and apartments because it saves the builder a lot of money when they are buying 100's at a time. The lower quality ones are more apt to give you trouble as well. 

Since you are only looking to fix one door lock it would be worth it to look over the available units and select one that is better quality. That often comes with a bit higher price as well. It has also been my experience that higher quality units tend to have a much more solid feel to them and contain few or no plastic parts.