Sarah,
Not to try to diminish the seriousness of your pain or the test but this is quite a common procedure. The HIDA goes by several names but is commonly called a gallbladder scan, and they are done everyday across the nation. The purpose of the hida, as you probably already know, is to determine if there is a blockage in the bile duct. This can be anything from fatty tissue to a tumor. (Don't panic! Almost all tumors are benign - non-cancerous - and not life-threatening.)
The good news is, it sounds as though you are in good hands. Your doctor is being thorough in his or her diagnostics.
The pelvic is simply expanding the search to a broader area (kidneys, bladder, stomach, uterus, etc.). Again, this test may find any one of a number of problems - almost all of them benign; almost all of them readily treatable. Those that are not? More good news, surgery can correct the condition and you should be good as new in a 6 - 8 weeks! In the unlikely (albeit possible) cases where more extensive treatment is necessary, long-term treatment is available and you should still be able to dance at your three-year old's wedding and babysit his kids!
The worst thing you can do is to worry and agonize over the worst case scenarios. Worry causes stress. Stress creates a chemical imbalance in the body & produces harmful enxymes into the system (which can result in ulcers and other problems). Even worse, if you do require surgery, the added stress can hinder recovery. So try not to stress. If you trust your doctor, take your questions and concerns to him or her. Ask what the long-term indications might be and what your options are for whatever the diagnosis. If you don't trust your doctor, or if your doctor is not readily accessible for conversation during visits, you probably need a new doctor... one you can talk to and confide in.
SOAP BOX ALERT: Don't ever feel you have to stay with a particular doctor just because you have been a patient for a long time. You are an equal (if not greater) partner in your health care and, if your doctor doesn't see it that way, you need a new doctor. Don't ever be afraid to question a doctor's dgX or to ask questions... LOTS of questions. Your doctor can only GUESS at what you are feeling and can only GUESS at how to treat your complaint. (How many times do doctors say "try this"? It's totally a guessing game because everybody responds differently to medications (and everything else in life!)) 'Try on' a few different doctors until you find the one that 'fits'. It's your health and your life. You need to surround yourself with people who will support that.
Good luck. Keep us updated.