When would you put in your two weeks for pregnancy?

I'm struggling with my extreme swelling & getting dizzy at work in my last few weeks. I want to keep working to save as much money as I can, but also everyday when I get out of bed I limp until my feet get used to walking again. I'm 33 weeks & I work as a bagger. which means standing for 6-10 hours a day, pushing carts, picking up heavy stuff. I just feel so drained. & I'm afraid he'll come early because me and my brother were both 4 weeks early so I'm scared he'll be somewhat early (not 4 weeks). Should I just wait and push through? Its only 6 weeks & 5 days. ivemade it this far :) maybe i just need to look at it in a positive way