A simply loose connection will not usually trip an unloaded breaker. A loose connection will get hot and fail with a load applied, but it sounds like you have an actual short somewhere in your circuit (wire has come clear out of a splice and grounded, or wires have melted or burned together, or you have a load on the circuit that you have forgotten about and it has become defective, or etc...).
What the guys above said rings true. Splices in junction boxes (if you have them) are a good starting point. This is also a good place to split the circuit for troubleshooting. Light fixtures and receptacle boxes next. And I too do not like back stabbed 50 cent receptacles, UL listed or not. They have a propensity to fail over time.
When you find an issue (and you will), clear it and re-try the circuit before you put everything back together... just in case one issue caused another that you didn't find yet. It's also a good exercise to re-check your entire project, since you know much more now (hopefully about everything) than you did two years ago.