Am I missing something here?

Why is my investment in the negative, if both the current share price and current sell price are above what I purchased for?

Plus the exchange rate has gone up since the time I bought!

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USD/GBP difference. You buy shares for a specific price and with a specific currency rate. When GBP goes up or down against USD, this will affect your result. Apart from difference in buy price and current price of a share.

If by exchange rate going up you mean the pound is worth more against the dollar then your dollar investments have to do more work to give an increase in value - 10 dollars is buying fewer pounds than it did before. You need the pound to weaken after you invest to increase your value in GBP if nothing else changes.