After 1 week umbilical hernia surgery, it is hard under the skin?

Yes: You will feel the "lump" that is part swelling and minor bleeding and part scar tissue formation. At the beginning of healing, scar starts off like a microscopic pile of hay.As the hay fibers get linked & stronger, the rest of the hay can be reabsorbed and the wound gets softer. The sensation of a lip or mass will then go away. Usually takes a few months to a year for all this to happen.

Mesh: It's probably the mesh. It is normal. Should soften up over time. Call your surgeon if the wound is red or draining.