Sleeping On Side

Abt 18weeks now and I've been trying to sleep on my side as I know that it's better for baby. But every night I spend 2 to 3 hours tossing and turning as I'm really not used to it even with pillows as support etc. Question is shld I keep spending 2 to 3 hrs every night to try get used to it or just sleep on my back and get more rest? TIA!