17 dpo and still bfn

Lucy • Mum of 4yr old little girl ttc baby #2
Should I have had a bfp by now if I was going to get one? Im not really getting any pregnancy symptoms although I'm very sleepy and getting the odd tummy cramp not like AF though. My periods can vary from 5-6 weeks I'm in between the 2 I'm worried it will show up in a weeks time and I'll be out as I'm getting bfn!! :( x