I had a grade 4, admitted to hospital at 36 weeks, not so much as a spot of blood. While I was lucky and others don't fare as well, don't panic about it, you'll have to have a long stay in hospital if it's a grade 4 but you'll be well looked after. Were you warned about pelvic rest? No sex unfortunately, but it's better to be safe than sorry.
As has been said before, most move, but mine didn't budge an inch and I have a calm and lovely C-section at 39 weeks. I lost a lot of blood during the c-section (common with previa) so was very anaemic afterwards but they stockpiled my blood while I was in hospital in case I needed it, I didn't as it turns out.
I advise you (and I'm no professional at all) to take it as easy as you can, bleeds can be very serious and not to be taken lightly. Get advice about working, I worked until I was admitted to hospital, but I did no significant lifting from the day I found out the dangers. You at least need to discuss your situation with your employer and see what they can arrange for you. You have a lot of rights as a pregnant lady, by all means make the most of them. Placenta previa is too serious to take risks with because someone needs a box moved, isn't it?
Good luck anyway, hopefully you just have a partial previa and that means you may still be able to have a vaginal birth.