Q. May one don a brand new suit during the Three Weeks prior to Rosh Chodesh if the sheheyanu was already recited soon after acquisition (one did not actually make a sheheyanu on the beged, but rather had them in mind when making kiddush on leil Shavuous?
A. Shulchan Aruch (O.H. 551: 17) writes that it is correct to avoid reciting shehecheyanu during the days of Bein Hametzarim on new fruits or clothing. Sefer Chasidim (840) and Magen Avraham (ibid. 42) explain that since it is a time of puraniot and disastrous events, one should avoid this blessing then.
Poskim disagree whether it is permitted to wear new clothing even when one is allowed to recite shehecheyanu, such as in Shabbos (Mateh Moshe 697, Mishna Berura ibid. 98 quoting Hagra), while others prohibit, especially if it is an important and significant garment and there is great joy in wearing it. (Eliahu Rabba – ibid. 17, Derech Hachayim – ibid. 6, Toras Chayim – ibid. 122, et al).
Horav Shlomo Miller’s Shlit’a opinion is that in your case or any other instance when no blessing is recited, such as when one blessed at the time he purchased the item, one should still avoid wearing significant and noteworthy new clothing.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a