Difficulty catching my breath during workout

I am a returning swimmer after taking 30 years off from the sport. I am swimming for fitness primarly. I have lost 180 lbs through diet and exercise but decided to start swimming to finish my weight loss. I still have 80lbs to lose. Typically I swim 2000-2500 yds per workout. The coach gives the team intervals that are very tight for me. Often times I get only 5-10 seconds between sets. I am having trouble catching my breath when doing freestyle. I do not have this problem if doing breaststroke or backstroke. Should I be concerned? I have been swimming for 4 months. As a side question, I still have 80 lbs to lose, plus lots of excess skin that needs to be removed. Would this be causing drag that is slowing me down? Thanks