Very strange thing happening. House is less than an year old. This is the bathroom circuit. The only modification was an additional outlet. Everything was working fine for months. Until this morning, woke up and realize the breaker tripped. When I tried the reset the breaker, it trips immediately. I turned off all lights and unplugged all outlets, then the breaker was able to stay on. Now the strange thing is, any load on the circuit trips the breaker. Flipping any switch or plugging in any outlet causes the breaker to trip. Any idea what causing this?
It sounds like a wire may have been damaged during the install. I am guessing at this point that it is a gfci breaker since it only trips with a load. In this case I would be looking for a skinned neutral or a point in the box that the neutral and ground may now be touching. I don't believe it would be a hot wire because it holds with no load, why did it start after months? Wires relaxing , home vibrations but at least this provides a location to look in the boxes on the neutral , it could be a staple in the wiring but I would check boxes first.
Check your new wiring for a N-G fault
This sounds like the classic symptom of a neutral-to-ground fault in wiring. I would check your newly added wiring to make sure neutral is not shorted to ground anywhere in it; if that doesn't reveal anything, then check the rest of the circuit for a N-G fault -- this might be a skinned neutral wire in contact with a metal box, excess tail sticking out from a receptacle screw, or some other sort of workmanship defect.