As far as your biceps workout goes, if you've been doing that same workout for a month or 2, it may be that your muscles are adapting to it, and might not respond anymore. Everyone needs to change-up their workouts after 6-12 weeks. You can certainly just add more sets to the existing workout, but that adds more time to your workout.
Another option would be do start by doing higher-rep work, say one set at your 15RM to failure to pre-exhaust your bicep, and then start-in on the higher-weight stuff. Another option would be to superset Chin-ups/Pull-ups with dumbbell curls. That should bust you out of your slump.
The other question is are you working your triceps enough? Your body will prevent one muscle from getting out-of-balance compared to the opposing muscle.
You might even want to give your biceps a complete break for a week or so. It might be that you're not allowing your bicep to fully recover between workouts, and thus never fully realizing the strength/size gains. Keep in mind, workouts don't make muscle stronger, it's the recovery afterwards.
Lastly, are you squatting/deadlifting enough? If you're not doing the 'Big-Lifts' enough, you're missing-out on growth stimulus for your whole-body. I like to start each workout with some variation of squatting or deadlifting, and sometimes at the end of the workout as well. As others have said, don't forget about chin-ups/rowing either!
The basic rule is that no workout works forever. If you start to plateau, change something.