Feeling like AF is coming at 6w after spotting

MissJelly
I'm 6w5d and yesterday had spotting. It wasn't a huge amount but it was red the first time and the next 2-3 times it was like brown CM. We went to hospital but long story short they could only do another beta test - levels came back 25700 after being 2202 the previous Wed.
​At the time I didn't have any cramping so they didn't do an US. Now all the preg symptoms I had are pretty much gone, except the lower back pain. And I feel like AF is coming - I don't have cramps as such I feel what I can only describe as sickly / really mild cramps in my lower pelvis area. Yesterday would have been the start of AF or the second missed AF since being preg. 
​Has anyone else had this? What was the outcome for you? 
​I can't call our IVF nurse or dr until Monday for more advice and maybe to do another beta. We've got a scan booked for Friday 15th but I don't want to wait that long to know what's going on.
​I'm so scared so any advice would be great!!