Does \usepackage{amsmath, amsthm, amssymb} statement in preamble affect linespacing in equation display in Latex? Without this \usagepacke, linespacings among equations were singlespacing, but if I use this usepackage for other features, spacing just double, which I am not interested in.
Please post a minimal working example showing this inter-line spacing change. The following simple code shows the same spacing with or without the amsmath package:
\documentclass{article}
%\usepackage{amsmath}
\begin{document}
text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text
\begin{equation}
a=b
\end{equation}
text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text
\end{document}
By the way, since your problem does not depend on TeXnicCenter, your post belongs to one of the subforums LaTeX->General or LaTeX->Packages and Document classes
text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text
\begin{equation}
a=b
\end{equation}
\begin{equation}
c=d
\end{equation}
text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text
\end{document}
Try to get the pdf. Just check the space between eq (1) and (2) printed. Now remove the \usepackage{amsmath}. Rerun and check the space between same equations. It's reduced.
When you use the amsmath package, blank lines will produce additional vertical space. The following example shows how to correct this problem: in the first pair of equations a commented out blank line was added for clarity's sake; in the second pair of equations no blank lines were used. If you want to preserve the indentation obtained leaving a blank line after an equation, you can use the \indent command:
\documentclass[fleqn]{article}
\usepackage{setspace}
\onehalfspace
\usepackage{amsmath}
\begin{document}
text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text
%
\begin{equation}
a=b
\end{equation}
%
\begin{equation}
c=d
\end{equation}
%
text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text
\begin{equation}
a=b
\end{equation}
\begin{equation}
c=d
\end{equation}
\indent text text text text text text text text text text text text text text text text text text text text text text text text text text text text text text
\end{document}
Remark: I removed the no essential parts of your preamble.