I have hypothyroidism since last 10yrs, on 100mcg of thyroxism sodium daily 1 tab, is it easy to fall pregnant or need additional treatment?

Same as normal: If your thyroid level is normal on replacement, your chance of pregnancy is generally the same as if you didn't have a thyroid problem in the first place. Depends upon your other fertility factors. There are some women, however, who have thyroid disease secondary to antibodies against their thyroid and these can cause uncommon fertility problems.