Usually on day 3 you feel weak because that is the height of the cleansing process. You should drink more lemonade though, it will stop you from feeling so weak and give you enough energy to work out. I work at my job all day and do a lot of walking for my commute and I have not felt weak since day three (I am on day 10 and still going). Day 4 was a jolt for me, I felt better than I had in years. Keep drinking a lot of water, do the P&B shakes if you want and drink MORE lemonade, I usually drink it all day long non-stop. Try doing a light work out and build up if you feel weak, stretching is great, it slowly works the toxins out through your stretched muscles! Good luck!