toenails turned black & fell off

I started going to a gym for weight-loss & fitness 3 1/2 months ago. I am 54 yrs. old. I work with the trainer twice a week & use the treadmill on those days & about 3 other days each week. A few weeks ago I noticed my 2nd toenail was black and it eventually came off. This morning I noticed I was missing the same toenail on my other foot. (I didn’t notice if it was black because it had nail polish on it). When it happened the 1st time I thought it was from a fungus. I haven’t had a pedicure in months & now I think it might be from the gym. I’m also wondering if I need to see a podiatrist or do I just wait for the nail to grow back?