P.R.
This is normal - second pregnancies are always harder than first ones because you have a child to look after, will have less time to rest, and have a lot more demands placed on you. I often feel lightheaded myself when I have too much going on.
I found out that sometimes asking my child if he wants to help difusses the situation - I'll give him a paper towel and a spray bottle filled with water and let him go to town "cleaning" the kitchen cabinets. Or I'll ask him for help cooking, letting him do safe things on a small table I keep in the kitchen.
Other times I need to lie down so we go into the bedroom and do storytime or watch a show on PBS (Superwhy, Martha Speaks and Curious George are good) that keep him entertained and gives me a break.
Another thing I do is to have "quiet time" each afternoon - he gets to stay in his room for an hour or so, napping, playing or reading (I have a baby gate in the entrance & a monitor). He loves this time and often asks for it when he's tired or overwhelmed.