Can i use anti histamine fenistil gel (dimethindene maleate) for a bite while i'm in very early pregnancy?

No major risk: Most antihistamines are considered safe for pregnancy (Category B) nowadays although I am not familiar with the product you are using. I do not expect any measurable absorption from the topical application of an antihistamine on the skin and thus it would be extremely unlikely that even if a trace of it gets to the fetus. A hydrocortisone cream would work better on an itchy insect bite.