At 18 weeks, my mother advised me to start sleeping only on my left side. My gynac also confirmed this helps with blood flow to the baby, so do try that.
I totally understand the beautiful mix of excitement and anxiety at this phase. You might start feeling those tiny, sweet butterfly flutters soon, which is just magical!
Oh, I overthought every single stretch pain in my stomach at 18 weeks! It's usually just round ligament pain because the uterus is growing, but write down your doubts to ask your gynac.
Around 18 weeks, I panicked because I couldn't feel any baby movements yet. But my doctor told me it's totally normal for first-time moms to not feel flutters until week 20 or 22, so relax!
Expect a visible baby bump and maybe some back pain starting around now. You should also start preparing for your 20-week anomaly scan, which is super important.