I am 36 weeks pregnant and have had back ache and period pains for 2 days now,could this be start of labour?this is my 3rd baby and didn't feel like this with the others.

All pregnancies and labors are different.

I know people who had back labor and they didn't even think it was labor,they just assumed it was the stress of the weight.

Yes,this could very well be the start of labor.

Best of luck to you and your little one !