It's not a silly question, but you need to explain a little more. Are you T1, and what is your starting BG. In short, going off the info given, I would guess that you need to time your insulin better. If, after 4 or 5 hours your BG has returned to the starting point, then you have taken the correct amount, but the raise was caused by taking it too late. Take it earlier (try 5 or 10 mins sooner) and see if it improves. If the final BG is higher than the pre food BG, then it is also due to too little insulin, so you need to check your Insulin to Carb (I:C) ratio and possibly it was too little insulin also. Hope this helps.