How can I relieve my 2 yr old. He has belly ache grabbing his butt and saying poopy. Can I give him a warm soapy water enema

Many medical and parenting sites discuss this in detail, so no need to write the book here.
Here's one
Toddler Constipation - WebMD: Causes, Symptoms, and Treatments (http://www.webmd.com/children/guide/toddler-constipation-causes-treatments?page=2)

Yes, an enema is OK.
If you want to come back here and tell us what his diet is like, maybe we can help with that.
I'd like to add actual good quality plant oil, a tablespoon a day, if he isn't getting dairy fat.
Some parents cut out fats and oils, giving their own diet foods to their child, when a toddler still needs them.
Other parents let them eat pretty much junk, white air bread and fast food and hot dogs and mac and cheese.