I change my clients workouts every session, nothing seems to keep the results coming faster. You don't have to change everything, but throwing in some variation keeps you from plateauing, makes things more interesting, and involves more muscle groups in more planes of motion. 4 1/2 months is a long time to be on the same routine, within weeks your body will begin to adapt and you'll get less benefit out of your workouts.
You can stay with weights if you wish, just change the protocols more often. Changing between circuits, supersets, burn-outs, low rep, high rep etc. You can also vary between split and full body workouts.Personal Trainer Los Angeles - Hollywood