It's called "transvestitsm" or in plain English, "crossdressing" and is engaged in by both men and women (Male to Female and Female to male)
It also falls under the overall heading of Transgenderism, which is the "T" in LGBT.
You could also simply have a clothing fetish, however that is usually limited to one or two articles of clothing. If you enjoy dressing feminine in different styles, underthings, etc, then you are most likely a crossdresser.
Crossdressing does not affect your sexual preferences. The Majority of Crossdressers seem to be heterosexual with about the same percentage as the general population reporting as homosexual or bisexual. In other words, if you fancy women before you dress, you will most likely still be attracted to women regardless of whether you are dressed as a man or a woman.
Estimates are that about 10% of the population could be considered crossdressers at one time or another. Technically, crossdressing is wearing anything that is considered the garment of the opposite sex, but as social tastes change, what is male (orginally high heels were on men's boots) becomes female and vice versa. Few people realize that men wore corsets in the 1800's as did women.
Nothing is wrong, you've just found a way to balance your yin-yang and discovered a feminine side that you may not have been conciously aware of.
On ebay in the American Girl category there are many people selling the clothes for American girl. I sold many dresses made by a lady in my area who was a wonderful seamstress. These clothes seem to be very inexpensive for the work that goes into them. Buy several outfits from one person so you can combine the shipping and make sure the shipping is reasonable.
New American Girl and her clothes with tags are only sold by the company. As to keep the price higher.
When you go on ebay do advance search in dolls bears only type in American girl, you will find all you need.
Best of luck