how much do i need to do?

i currently ride about 2 or 3 times a week for about an hour each time at a hardish pace with alot of short sharp climbs. is this enough to build my fitness as im fairly unfit anyway? i am slowly losing motivation because im alway tired at the end of rides so my fitness does not seem to be improving. :?
2010 Forme Reve
2010 Giant Talon 1
2010 Giant Talon 1
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At the moment I'm doing 3 interval sessions during the week (about 40 - 45 mins each). Then at weekend do two longer, but fun runs to build up general stamina but more to have fun. These tend to be between 15 and 20 miles but I don't try to push hard. Just enjoy myself.
http://cjwoods.com/london2paris
Scott Scale 10
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