This is not necessary, but if you like the tea, it's certainly okay to keep drinking it. Fenugreek is an herb that is often very useful in increasing a mother’s milk supply. It is frequently combined with blessed thistle to increase its effect. There are many teas on the market that contain one or both of these herbs that are intended to increase milk supply. It can be helpful to drink one of these if your supply seems to need a little boost, but is really not too low. Once your supply is where you want it to be, there is no need to continue drinking it.
However, if your supply is low enough for concern and you're trying to increase it as quickly as possible, then you should consult someone about taking these herbs in capsule or tincture form. It's important to know the exact dosage you should be taking and to be consistent with it. With tea, it's almost impossible to really know the dosage in each serving, and the amount is generally much lower than in concentrated capsules.
If you have certain medical conditions you should not take fenugreek, so be sure to consult with your doctor before starting higher doses on your own.