Hey Jessica! Congrats on your triathalon!
Anyway, I had the same problem. My weight gain was attributed to a lot of inactivity and severely eating off plan. However, I noticed that just getting back on plan wasn't working all that well.
I started losing weight when I increased my cardio to a shorter morning session (20-30 minutes) + a longer evening session (30-45 minutes).
I had also been eating carbs pretty regularly (rice was becoming a big staple) and had been grazing.
What got me losing again eating-wise was limiting carbs in the evening, not eating after my evening workout, and eating a more standard 2-3 larger meals a day. Obviously, this goes against the grain somewhat, but it was enough to shake things up for me
Also, maybe venture into specific plan territory - like SB or WW. Perhaps you just need some more structure?