Is it possible2have an umbilical hernia w/o a visible lump? what else can be the cause4occasional pain inside belly button? (esp when bending back)

Umbilical pain: Pain inside your umbilicus could be a symptom of a small hernia. There are some other possibilities. Okay to check in with your doc. An ultrasound of the abdominal wall can be helpful.

Strain: Yes it is possible but it could be abdominal strain. If you have a hernia see a surgeon and they will fix it.

Yes: A small umbilical hernia can be present and not felt or seen. But most surgeons can detect them by feeling. It's more difficult if people are very heavy.