I would suggest you leave the shampoos alone for awhile.
I find that most of them strip the hair of natural oils that it needs for elasticity, porosity and strength.
Try an overnight oil conditioning treatment with castor oil.
This oil has a tendency to be sticky, but is excellent for adding sheen, retaining moisture and suppleness.
Often when hair is lacking in sheen and is dry and brittle we are lacking EFA in our diets. Essential Fatty Acids.
Try Flax seed oil, Fish Oil, Borage Seed Oil.
Flax seed oil is excellent for oil conditioning treatments as well. Apply to hair for 40 minutes using a steam towel treatment. Rinse with warm water for six minutes.
As for a itchy scalp. Emu oil is excellent for itchy scalps.
Make sure that you are not suffering from a conjested scalp.(overload of products) by using a clarifying shampoo. (pea size amount) on scalp only. To remove any products. To many product left on the scalp will clog pores and make scalp itchy. Follow up with a moisturing shampoos like Break Thru by Soft sheen carson.
Just a small amount to soften hair after using clarify shampoo. Leave on for 3 mins.
I would not use the Henna. Henna is excellent for strength and contains alot of protein. I know alot of women suggest using protein to stop breakage. I suggest something different. Protein will add stength and make hair hard with usage and brittle if used too often. This seems to be your problem now. So wouldn't protein contribute to brittleness and dryness even more.
Suggestion: Moisture, Moisture, Moisture,
Castor oil. (just a little) do warm water rinses for about 3 days for 6 mins. Focusing on stimulating scalp. Keep your hair products to a minimum. Also try Regis Hydrating Balm for 60 mins under a hooded dryer. EXCELLENT for moisture restoration. Try adding a bit of olive oil to it as well and heat for 23 secs. Then go under the hooded dryer.
Keep scalp clean. Apply light oils such as avocado oil or jojoba (wax) to add moisture and softness to hair. Africa's best Ultimate oil is a great product. I add just a tad bit more jojoba to it.
Alberto VO5 Hair Therapy does a excellent job of giving hair slip, detangling and protection against heat if you blow dry. Throughout the day you may try just a spritz of water with cator oil and jojoba.
Try not to overprocess hair and keep relaxing to a minimum.