The Library of Congress Digital Collection is a wonderful resouce for primary sources. Note the field on the left of the webpage. You can search by
If you use the dropdown menu at the top, you can switch from Digital Collection to Personal Narrative. In personal narrative, you will find interviews with people, and in particular a large selection of interviews with veterans.
ProQuest's Historical Newspaper database has full coverage of 36 newspapers going back into the 1700s, most articles are from the 20th century, however. Newspapers include The Washington Post, The New York Times, The Wall Street Journal, and other well known publications. Depending on your topic, you might prefer a regional newspaper, such as The Atlanta Journal or The Chicago Tribune.
Photo by beanworks at Morguefile.com, used under creative commons license.
The National Archives have a rich set of data, but it might take a little more digging to find. You can search in a search bar, but also within collections such as War and Military Records, Founding Documents, specific places or subpopulations such as Women.
The Primary Source Sets of the Digital Public Library of America (DPLA) are curated around specific topics. Each set contains numerous primary sources including images, music, interviews and more. There are many, so you will need to scroll through to see if your topic is included.