Theres a few things you can do to gain strength to your arms...
1) dont do reps, go by time.. such as if you are curling dont go by how many reps your doing, set yourself a time for how long you will curl... I do 40 seconds as 1 set of a curl so aim for around there it will be your best results.
2)resistane training, the new popular training for professional athletes is resistance weights.. many NFL players such as Steven Jackson, and most of the Rams do this because It adds so much strength.. they do theres in aqua gyms, which I imagine you dont have access too so the easiest way for you is if you train with another person have someone put some force on your weights, trust me when someone puts some resistance on a curl or bench your gunna feel it.
3)Curl, curl, curl, curl, and do some more curls.. there are so many curls you can do that people don't just because they believe oh, well a curl is a curl.... no, do them all go to a gym and get a list of the 8 curls, and do them once a week....
However, you may think you arent getting bigger but you probably are, your body just gets to a point where it does not go through the same weightlifting stages it did... once you get over the soreness, and the sickness of a very intense workout your body is pretty well use to working out so It wont go through the same stages that it did.