Increased reasting heart rate (around 100bpm). Need advice please. Does anyone else has this?

I played basketball, I'm 18, and my case sounds very similar to yours! I would get really tired during exercise and have trouble breathing. My resting heart rate is normally right around 100 but it has gotten up to 120 before. I have tachycardia and an arrhythmia. My blood tests showed no thyroid problem as well! I too had a 24 hour monitor and tried beta blockers which lowered my blood pressure too low. I am having to have a procedure called an ablation done soon, because without it my heart muscle will eventually start to weaken! Good luck!!