I have dealt with this obsession in past,this obsession was one of the obsessions which were hitting me due to ocd.
you are taking medicines already, so keep on taking them as your doctor have prescribed .
It can take months to fully recover but you will see the signs of recovery in few weeks, things will get better with time.With medicines you will have to learn cognitive behavior therapy,you can learn it from a psychologist or with help of book "Overcoming Obsessive Thoughts: How to Gain Control of Your OCD" by christine purdon,this book is really helpful for pure o sufferers.
Regarding this obsession some things you can do are-
1)focus on your breathing for some time like (2mins),you can increase time by practice, it will act like a exposure for you,when you expose yourself to your breathing the anxiety associated with it will decrease it
2)do some physical exercise like jogging ,brisk walking for some time so that your breathing becomes fast now focus on your breathing.
These exercises will help you in the treatment,you can do them when you are free and do them regularly.