Your doctor is encouraging you to get up to 50mgs because it is considered the minimum effective dose. If 25 mg is working for you, then by all means, talk with your doctor and suggest that you hold at 25 for the time being.
You may find that 25 mg works long term or you may find that your body gets used to this and that you need to eventually increase. Either way... If 25mg is doing the trick for you now, I would be hard pressed to increase for the time being.
You may want to buy a pill cutter and take 12.5 mg in the morning and evening to maintain good, steady blood levels. (Then again, as the saying goes... If it ain't broke, don't fix it).
best of luck