4 weeks, bad cramps no bleeding

I'm only 4 weeks,  bad period like cramps no bleeding.  They can't see the sac yet,  I'm hoping they will next week.  They don't think it's ectopic but who knows this early.  Some light brown discharge here and there but nothing heavy. Also bad ache in lower left back.  Ive had 1 miscarriage before but i was bleeding from the start.  Anyone else experience something similar? Hcg very normal and rising normally.