20 weeks no movement?

I thought I was feeling the baby move around 17-18 weeks, despite having anterior placenta but over a week has gone by and I haven't felt anything. Was I wrong at first and just mistaking gas or similar as movement? Is it weird that I'm 20 weeks and haven't felt the baby in a week (or maybe at all?) I have a regular  sonogram scheduled later this week so trying not to stress out, but wondering if I should move it up to sooner. No other "bad" syptoms  to indicate something is wrong. Anyone experience similar?