0.5s query takes 13s to run 4 times

[eluser]sigsauer[/eluser]
the query is just slow... I checked with

$this->output->enable_profiler();

SELECT AVG(price) as price, week from globalhistory where product_id = 1 and week > 1098421200 GROUP BY week

this query takes 4 seconds to complete... not sure what to do now.