Vietnamese here. It's hard for me to find an English source, but I'll provide what I know.

After the war, like other communist states at the time, Vietnam nationalized most of the economy and started projects in hope to industrialize the nation. Although some infrastructures were built, this policy led to an economic crisis, many people in the South lost their business and left the country.

There was no mass-murder as many people had feared, but former South Vietnam soldiers were asked to go to "re-education" camps. Some of them went home after a few months, but some were kept in those camps for years. Most of these people and their families also left the country afterwards.

Vietnam also was dragged into a war against China and Khmer Rouge from 1978 until 1989. While many people see this war as a necessity to protect the nation's sovereignty, it again hampered the economy. Vietnam depended a lot on supply from the Soviet Union and Eastern European countries.

In 1986, the government opened the market and followed a more flexible diplomatic policy, similar to what happened in China. I would argue that the real "reconstruction" only started from that point and is still happening today.