Testing negative while having all the right symptoms

I had a mc june 8th. Since then i have not had a period i keep testing but they come out negative. For about a month or so ive had cramping and lower backpain aswell as alot of heartburn. Ive never had heart burn.. so today as i was at work, i felt as if i was going to faint throw up and just completely felt horrible. Ive heard some people have been pregnant while still testing negative on urine tests. What should i do? Anyone else gone through somthing similar??