New and motivated in Missouri

Hi!  My name is Alana and I have finally decided to go for it and try my first Sprint Tri.  I have been looking at me events in my state and have found I will probably have to wait till next Spring unless I want to go out of state.  I am very new and I have not been  physically active since before my son was born in 2002.  Prior to that I was very active and athletic.  Now I am sluggish about 30lbs overweight, bored and tired of feeling tired! I decided my son needed a more healthy role model and needed to feel better about myself at the same time.  I work in a busy ER and I am seeing younger and younger people on multiple medications, having serious health problems and even dying all as a result of their habitual inactivity and prro diets.  I did not want this for myself.  I have started walking/running on my own and riding my mtn bike (already lost 8lbs) but have found I need a bit more guidance.  I have looked at the training plans and a bit intimidated by the job of choosing the correct one.  I work 12 hour shifts 3-4 days a week and I know I can get myself up to run those days but pool and bike workouts would be more difficult due to the pool hours and the fact it can pitch dark out when I get up or get home depending on the season.  I know there are others out there that work crazy hours and are doing it and I refuse to let my job get in the way...any tips or ideas???