If you think they are due to farrow early next week they will be changing now at the back end with the vulva becoming larger. Are you farrowing outdoors or taking them into separate areas for farrowing? If you are planning to separate, which I would advise, then I would do that now. As they approach farrowing they are happy to move into their own space.
If you don't separate then they will look for somewhere quiet, which might well be out in the paddock not in a shelter.
As SophieLeeds said they will generally make a nest. Some of mine do that and get straight in and farrow. Others make nests for a couple of days. Some don't make a nest as such just move the straw around. Too much straw is not a good idea, especially if it is long. When they nest build they tend to add in anything to hand such as water troughs if they are moveable so they potentially end up with a wet bed.
A sow needs no more extra food until she progresses through lactation. Again leaving food in there it will probably get mixed into the bed and later the sow potentially will dig up nest and piglets to get to it. After farrowing, when the sow has fed the piglets I put in some food and water and she can please herself.
Often but not always, not eating their food is an indication farrowing is close. Some sows won't eat much for a couple of days either. Some are ravenous.
Very, very few farrowings are difficult but especially first time gilts can be upset by people going in and out and will get agitated, so watch from a distance. OSB are generally very good mums. Use your board. Close the door behind you but don't latch it then you can get out quickly if you need to.
The clod of earth is a good tip for iron as sow milk is deficient.
The easiest farrowing is when you go down in the morning and the piglets have arrived already!!!