Worried about heavy lifting

I have a job where I have to lift heavy boxes well not so heavy around 16kg it's just more awkward trying to lift them from in a trolley and I'm just worried about straining myself! Does anyone else have jobs that are physical ? This will be my 4th child but I did miscarry 2 months ago and would be devastated if it happened again! I do bend my legs when I lift and really try to be carefull.