Baby movement not as strong as before

I'm currently 23 wks and for the last week or so I notice that booboo's movements has been really weak compared to before. Ie. before I could feel it from the outside. Now, I still feel her move around but it's not as strong and I can't feel it from the outside anymore when I put my hand on my tummy. Also, I find that she moves less as well. I'm really worried. Has this happened to anything else? Or should I call my midwife? Thanks.