Again, do a search, I am sure you will find Coder's Guru's lessons. There is nothing better than learning how to do it right.
I am providing you with a subroutine that will count the number of trades for a given symbol and a given magicnumber. You can call that to find the number of trades, and if it is equal to or less than a certain number, you can place your trades.
PHP Code:
int CountTrades(int MagicNumber)
{
int count=0;
int trade;
for(trade=OrdersTotal()-1;trade>=0;trade--)
{
OrderSelect(trade,SELECT_BY_POS,MODE_TRADES);
if(OrderSymbol()!=Symbol() || OrderMagicNumber()!=MagicNumber)
continue;
if(OrderSymbol()==Symbol() && OrderMagicNumber()==MagicNumber)
if(OrderType()==OP_BUY || OrderType()==OP_SELL)
count++;
}//for
return(count);
}