My quad muscles feel weird- 23 weeks pregnant

I’m 23 weeks and I was going down my stairs and my leg felt like it was going to give out. My quad muscle felt like I had done an intense leg work out (for those who squat heavy- you know when you squat your max and then yours legs feel like jello). I obviously am not doing any crazy works outs or any leg work outs at that. Does anyone know why it felt like that? It feels pretty tight and sore now