First off, make sure you are eating food... Best bet is to have a meal and a snack going at the same time (you can see which ones are which by reading their tooltips) and you can also carry "instant-heal" foods such as Bacon (you can put those on your sidebar) for a health and power bonus that is limited by your Metabolism

Food gives you in combat and out of combat bonuses, and its very important

Combat Refresh refreshes every 15 seconds while in combat, and it will add the total of all the in combat bonuses you have available from your gear and food, but you have to use a "basic" skill to get the bonuses

For Sword, the basic attacks are "Sword Slash" and "Thrusting Blade," and when the combat refresh is available you will see those skills (if you have them on your bar) flash with a blue icon... there is also a combat refresh sound signal

Once your combat refresh is available, using a basic attack will dump all of those stat bonuses back into your active stats, which can literally be the difference between life and death in a fight

Try watching for those signals and see if that helps... If that's not the problem, all I can think of off hand is that maybe you de-selected your enemy in combat somehow

If the issue is not actually related to power, we may need to talk about how you are selecting enemies in a fight I guess