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Only rush Doran Blades if you plan on ganking a lot. Otherwise, you'll be wasting your gold. 2 Dorans should give you enough HP to still tank the tower while killing the opponent faster.
You may also be too used to having that amount of extra HP. You need to be able to adapt and understand that while you can't take as many hits, you'll be dealing damage faster. So wait until the opponents are farther from their tower than you normally would, etc.