@ysmina-- It may actually be difficult to tell them apart without seeing a doctor. Although you could try elimination to try and figure out the exact cause of your symptoms.
In addition to inflammation and itching, vaginal dryness may also cause flaky skin, irritation and redness. Also, do you experience pain during intercourse? This is another sign of vaginal dryness.
I guess we could separate vaginal dryness into two categories. There is vaginal dryness that occurs internally, due to less natural lubrication. You might have painful intercourse and itching at the vaginal opening in this case. The other type of vaginal dryness is one that only occurs externally, on the outer vaginal skin. If you have itching, redness, inflammation, irritation or flaking on the outer part of your vagina, it could be general dryness or an allergic reaction.
If you are only experiencing dryness on the outer part, try switching to cotton underwear and hypoallergenic soap, shower gel and laundry detergent. Also avoid perfumed pads and panty liners. Use a mild, scent-free moisturizer on the outside of your vagina for moisture. If your symptoms go away after these steps, it shows that you were having an allergic reaction.
I'm not a doctor though, I'm just speaking from experience. So see a doctor for a diagnosis and the best advice on treatment.