I drink one diet soda a day to satisfy my sweet craving will it effect my weight loss in a bad way?

Probably yes! Women who drink 12 oz. Diet soda have a 33% increased risk of type 2 diabetes & those who dink 20 oz. Have 66% increased risk! they cause increased Insulin release, slow metabolism & cause cravings for carbs. Studies show diet sodas are even more unhealthy than sodas with sugar, which are also really unhealthy. Avoid both! http://www.Huffingtonpost.Com/dr-mark-hyman/diet-soda-health_b_2698494.Html.
No. Some researchers and diet gurus do not like this due to triggering body's response to sweet (even though no sugar), but in long run, better to be happy and for majority will not make that dramatic of a change in rate of weight loss.