Visual Studio not building correctly - c++

Question

I've been having two different problems when trying to compile a C++ project today.
Sometimes it won't reflect any of my changes in the new build: If I change some wording on the output or change around actual functionality and compile and hit Start Debugging, it will behave exactly as it did before I made the changes. Hitting Clean or Rebuild Solution fixes this, but it takes about a full minute to compile this. I guess it's not detecting any changes, but in the output window I see it list the file names of files I made changes to...
I'm also getting a lot of "...already defined in main.obj" errors (one for every function and variable) whenever I try to use a header file or define a function outside of a class. Renaming the functions lets it compile once, but then the second compile will bring up the errors again. It kinda works if I just define the class in a .cpp file, don't use a header file, and don't use any functions outside of the class.
The project is an open-source program I downloaded the other day to mess with (I'm building a bot to control it). I didn't have the first problem until today, but the second one's always been happening. All I've done is add a file (two if you count both Bot.cpp and Bot.h); Bot.cpp includes Bot.h and some files from the program, and the program's main.cpp includes Bot.cpp.
I'll post some code I guess, but I can't find anything wrong with what I'm doing. I'm wondering if there's something I need to do to the existing files? (there were VS solution files included with the project that I used to open it, since VS Express doesn't help you create projects from existing code.)
//Bot.h
#ifndef _Bot_h_
#define _Bot_h_ 1
#include <string>
class Bot{
private:
uint32 inputs = 0;
bool active = false;
public:
Bot(){};
~Bot(){};
void Start();
void Stop();
void Run();
void Wait(int seconds);
void Press(int buttons);
};
#endif
//Bot.cpp
#ifndef _Bot_cpp_
#define _Bot_cpp_ 1
#include "main.h"
//Some other project files included between these
#include "Bot.h"
using namespace std;
void Bot::Start(){
if (active == false){
active = true;
Run();
}
}
void Bot::Stop(){
active = false;
}
void Bot::Run(){
while (active == true){
printf("Has my code updated?\n");
Wait(2);
}
}
//There are more functions defined here
#endif
All I've really done in the original source code is include Bot.cpp at the bottom of the list of includes in the main.cpp file, and then add a call to create the class. I'm a little out of practice with C/C++ so maybe it's something simple. I'm also bad at writing posts like this so if anything needs clarified I'll try to help.