There's various ways to do this. You need to keep track of the most recent position, or it's entry price. I'd create a field for the entry price of the most recent position in the symbol script class, and then put the following in the OrderFilled method:
if (trade.TradeType == TradeType.OpenPosition && trade.Order.OrderState == BrokerOrderState.Filled)
LastEntryPrice = position.EntryPrice.SymbolPrice;
Then you can check to see if the current price is greater than LastEntryPrice in the NewBar() method. You may also want to have a condition to reset the LastEntryPrice after a certain time or number of bars or something. Otherwise even if you made a profit on a position, you won't be able to open another one any time the price goes below that entry price.