Need help & hope...

I am 5 weeks today, first pregnancy, and just felt off from the time I woke up. My nausea & heartburn subsided over the last few days, discharge changed from clear to opaque & yellowish, went from being constipated to having diarrhea, and the pain in the left side of my lower abdomen seems to get a little worse every day. Went to the ER. Hcg level was 3448 but they couldn't see anything on the ultrasound even though the doctor felt like they should. We are on vacation so he said to go have my levels checked and get another ultrasound as soon as I get home on Monday. He is concerned the pregnancy is ectopic. He also said he's had women in the same condition and they were able to find a heartbeat in the uterus 2 days later. I want to stay positive but I just have a gut feeling this isn't a good pregnancy and my heart is broken. Has anyone had similar experiences that resulted in a healthy pregnancy? My husband and I could use a little hope.