I am really struggling with my ds. He is challenging everything that I tell him. I am trying to be consistent and firm but at the same time loving. He directly defies me unless he is totally occupied. He seems to get bored after only a few minutes and staying in the house is near impossible! What am I doing wrong???
There is a little jealousy with the new baby and that is contributing to the situation for sure. But I can't stand the whinning and the scowling at me when I tell him something that he doesn't want to hear. I am at a loss and really stressed out by it. I have had to pull over in the car to spank because he was doing a really loud scream that I gave him a verbal warning for. Then the other day he did it again and before I could even warn him, he spanked himself!!!! Not sure what that meant...
Any advice about discipline at this age would be greatly appreciated.

First off I would recommend reading The Strong-Willed Child by Dr Dobson and Bringing Kids Up Without Bringing Them Down by Dr. Kevin Leman. They are both great books and have helped me tremendously with my oldest daughter.

Also this might be a phase where because of the new baby he may be trying to get your attention. He may feel like you "love" the new baby more. I don't know how old he his but he may need reassuring from you that you still love and want him around. Kids this age are tricky because they will use negative behavior to get attention.

Stay consistent and firm. It sounds like you are already doing this and that will help in the long run. One thing I had to do with my oldest was to take her on a mommy and me outing where it was just us and we were doing something fun.

These are some thoughts I had. Hope everything gets better for you soon.

I am not sure what to suggest as I too have a very strong willed child and at times find it very very frustrating. This is the advice that I was given to help but not sure if it is any good for you:

If asking the child to do something ask no more twice then you take them to do what you have asked.

Ignore any behaviour that is not dangerous.

Give controlled choiced, for example 2 types of breakfast and ask what they would like, you can do this for many things.

Only give a set amount of time for meals and then if it is not eaten by then it gets taken away.

Be Consistent.

Just a little encouragement. A strong will can be a good thing if you can harness it. I would think that many of God's servants had strong wills, but God (and maybe their mothers :-D) worked with them to channel that will into service.

I knw from experince that with Sinead strong will come a mass of talent and she is very very gifted. I knw that I am truely blessed with her and that all the trouble we have is nothing compared to the joy that she brings.

Yes having a strong-willed child can be a blessing later on. My pastor's wife was so encouraging when she told me strong willed children are less likely to cave into peer pressure when they're teens than children who aren't.