Eh ye, quite a few of us felt that way at that stage! It's likely the baby's weight pressing on the vena cava (the big vein) when you're flat on your back, so side-lying je yang comfortable, totally normal at 33 weeks. Since your doctor is monitoring it and wants to check in 2 weeks, I'd stick with sleeping on your left side and avoid the terlentang position for now; if the dizziness gets worse or you start feeling faint even when sitting, definitely give the clinic a call earlier lah, jangan tunggu 2 weeks.