Sleeping

Why is it advised to sleep on the left side while pregnant? I toss and turn all throughout the night I go from left to right to on my stomach to on my back and it repeats lol. Is that bad to be switching like that? It’s uncomfortable to sleep but it’s been this way before the pregnancy it’s just a little worse now bc I have insomnia throughout the night but sleep like a grown man working 16 hr shifts throughout the day 😂