I had my first fill at 5 weeks post op, nil by mouth for 4 hours before (this varies by provider so check with yours), went in, quick weigh, and then led on the bed. She had to feel around to locate the port and this for me was the most painful part, in fact it was more pain that what I'd felt anytime post surgery.
She attempted to go in with the needle 5 times until she finally got to the port, the needle didn't hurt and I didn't feel anything going in or indeed the needle coming out, it was just the pressure of pushing down before hand that was the worst.
I had another fill 2 weeks later, I was in, led down, needle in and out, no pressing no pushing and all was fine.