Constipation on formula

My 10 month old is really having trouble passing her stool.  The stool itself is extremely dense and when she struggles mightily, only the smallest amount will come out.  Over the past three days she has really only had 1 movement of any size.  The rest of the time she struggles and not much at all happens.  Is this something to worry about?  If so, what can we give her?  The pharmacist recommended pedia lax (liquid suppository). The only change to her diet has been yogurt for a day, and we are moving to mainly formula as mom is running out of milk.  Could it be the formula?  She has been on it for a while, but is was usually half breast milk half formula.  Now mainly lactose sensitive formula with iron.

Your daughters constipation is likely due to the increased amount of formula in her diet. Unfortunately, increasing the amount of breast milk is not likely an option.

When children are uncomfortable secondary to constipation I usually recommend glycerine suppositories for immediate relief. These are bullet shaped pieces of wax. They come in three sizes adult, children’s and infant. While the adult and children’s can be cut down to size, I would try the infant size. These can be purchased without a prescription at most pharmacies.

Before inserting the suppository, hold it in your hand to warm it up and melt the outside. After it is inserted, most children will typically stool in the following 30 minutes. If she does not stool try one suppository a day for three days.
Chronic use of suppositories can create dependency. If she needs these frequently or they are ineffective please discuss this with her doctor.

The first thing you need to try to help her long term is dietary changes. Increase the amount of fruits, veggies, fiber (see fiber in diet) and water in her diet.
If dietary changes are not effective in relieving her constipation than she probably need medications.  When starting medications for constipation, I typically start with a class of medications called non-absorbed sugars.  These "medications" work like a diet soft drink.  You eat them but the sugar it is not absorbed.  As these sugars pass through your intestines they draw in extra water and loosen the stool.
 
My favorite over the counter non-absorbed sugar is milk of magnesia (MOM).  There is no set dose for MOM, it is dosed by effect.  I usually start with a teaspoon a day and adjust weekly. The goal when treating constipation is to obtain one to two peanut butter soft stools daily.