Pregnant but nothing in ultra sound

I have taken 4 home test, the first was negative and the rest were positive but the line on them were really faint, i went somewhere for them to test me and they did two test. She said they were faint but are positive. So she scheduled an ultra sound two days later and said i should be 6 weeks and 4 days along so there should be a baby, yolk sac and heartbeat. She didnt find anything in my uterus but a little thing here and there and said that might be it but not sure since it is so small, if it is the baby then i might only be 3-4 weeks along. But since the test found hormone in me i am still considered preg, but I am on precaution for miscarriage and ectopic pregnancy. She said to get a blood test done to check my hormone but i dont have the money for that. Any idea or opinions on what could be happening?