Very excited to start

Hi, I'm brand new at this. I'm a 27 year old girl from Montreal.

I've been working out (cardio and weight training) regularly for the past 3-4 years but I need a new goal other than "looking good" and "be in shape" because these kind of goals are not good enough motivators anymore.

I plan to do my first triatlon next May or June (I live in Montreal so I can forget about competing before that). I just want to finish it... no goal about timing or anything else.

I downloaded a 10-week beginning traing program from the internet to get me to the shape needed in order to start the 18-week intermediate program that I plan on starting in January or February (to get me to the triathlon day).

So far everything is good. I run 3 times a week, bike 3 times a week and swim twice a week for a total of 6 days of training and 1 day off (swim and run are on the same days).

My main concern so far is about nutrition. Since I was mostly into fitness before, I was doing a diet with minimum carbs possible FOR ME (about 150 grams per day). Now with so much cardio, it simple isn't realistic. I was also eating a lot of protein. What should I be changing about my diet? Will I gain weight if I start eating more carbs? How many calories should I eat per day? I'm 5'8 and I currently weight 125 pounds.

Also, any major tip I need to know before it's too late? The kind of thing that any new beginner should know?

That's enough for now but I will certainly keep bothering you with more questions...lol