The quantatative beta-hcg will give a number to the human chorionic gonadatropin level.
Sadly, even that doesn't assure a pregnancy as their are some tumors which produce this hormone. While your local GP may be adequate to draw a blood level, s/he isn't really trained in all the nuances of gynecology, so a real gynecologist is what you need.
"In the olden olden days just having your period stop and your belly get big would be enough."
Yes, this is true, and sadly some of those women died of reproductive tract cancer because everyone just assumed that they were pregnant. Or they had a complicated pregnancy that ended in the death of both the fetus and the mother. It used to be that up to half the women who got pregnant died either during pregnancy and delivery or shortly thereafter.
You need realize that "modern medicine" isn't out to get you, but there to help you. There are things about this situation that just don't add up. You haven't had a period in six months. You say you've got a growing something inside and feel movement, and yet you still have a negative home pregnancy test. Women normally wouldn't feel movement in a first pregnancy until somewhere between 18-22 weeks. At that time, a home pregnancy test should be so positive that there's no question that it's positive.
Please, you need to get to a gynecologist to see what's going on. If you have a growing mass, it needs to be diagnosed.