Someone please, please help me!!!

I love my children, and want to spend more quality time with them......

I have a divorce decree from Alabama, ex-spouse has custody. She and my children have resided in south-central Louisiana for 15 yrs, and I have resided in Dallas Texas for 11 years. My son is now 18, and my daughter is 15. Divorce order states the following:

"Parties agree that Petitioner (that's me) shall have the right to have the children visit with him at reasonable times for reasonable periods of time upon notice of at least two weeks first being given. Parties agree to work together on holidays, birthdays and other appropriate visitation periods."

She refuses to work with me on visitation.

I want my daughter to visit for 1/2 half of her summer vacation. Ex will not agree. She says that my daughter wants to work a summer job and does not want to visit but for 2 weeks. I also want my daughter to visit for at least one half of all State holidays which coincide with a weekend (three day weekends).

Can my ex-wife just refuse to allow my daughter to visit for what I consider a reasonable amount of time?

Should my daughter working a summer job be allowed to interfere with my visitation?

Which state agency do I contact to petition a change in my visitation order, and which state (AL, LA, or TX)?

Am I required to be represented by an attorney?