I don't think anyone will be able to diagnose/treat your child's problem over the internet. This is definitely a case where you will need to take her to the doctor. If your doctor won't see her till April, go to another one.
It sounds like an umbilical hernia, but you weren't clear on how long it has been this way. Since birth? For the last week? Month?
(If it is an umbilical hernia - which is something that is apparent at birth - it will go away between the ages of 2 and 5 years. Maybe sooner.)
Also, they should be seeing your daughter soon for her 9-month well-check. Sounds like your pediatrician is either really overloaded or just negligent - whatever the case, do try to find a new doctor and get her in ASAP.