How to get the biggest improvement?

I have been doing the same workout routines for like 3 months.....
I do see some results.....
As in that I feel much easier to lift my dumbbells.....
But my dumbbells weight just maintain there.....
If i increase the weight......
The reps gone down about 30 to 40%.....almost half of it.....
Is that means i cant actually increase the weight now of izit possible...
Is dumbbell workout focus only on my arms and chest?......(i think so coz so obvious haha)
Now I was like imbalance on my upper body compare to my abs and lower body......
Somehow it could give an impression to others that my body size were large......
But its imbalance......
I finding some other ways to work on my abs and lower body.....
Besides doing workout on these parts......
I have chosen to go for badminton and basketball....
Cause its fun and not so boring ......
Doing workout alone is so bored and dull.......
Sometimes is not too tiring to continue but its too boring haha.....
I hope that anyone who read my article could provide me some guidelines to solve my problems..
I appreciate if anyone could give me a help...thanks
^.^