BCRider

Assuming the pressure is OK then it is likely one of two things or a bit of both.

First off the tires. I've found that good tires that roll easy have a fairly thin and smooth tread face and a thin and very flexible sidewall. If the tire is thick and especially if the sidewalls are thick the tires can suck energy from you like a black hole pulling in light. There's any number of performance tires that will work on your hybrid. If you're doing road only I've had excellent results from Continental Super Sports. They are inexpensive as performance tires go and roll like they have built in engines. Panaracer Pasela is another option that I've had good results with and they come in a kevlar belted flat resistant version that really works. If your riding involves some loose dirt here and there then a cyclocross racing tire would be an option. Sorry, no direct suggestions on that front.

The other biggie is the fit of the bike.

The big one is that you want your saddle high enough that your knees almost fully extend but don't quite allow the knee to lock over center. Play with the saddle height until you can pedal with your legs almost fully extended but not to the point where you feel like you have to rotate your hips side to side to reach the pedals.

Being a hybrid if it's one of the comfort cruiser hybrids then the saddle may be too far back to let you really drop your weight onto the pedals. If it's one that has a soft seatpost then this is almost certainly the case. In that case you would want to do whatever is needed to shift the saddle ahead more. There's info around about how your knee should be directly over the pedal axle when the cranks are level. That's something to try but you can also do it pretty decently by feel. When you pedal it should feel like the pressure is lifting you mostly up off the saddle with only a little push to the rear. When the saddle is too far back, like on quite a few comfort hybrids it'll feel like your pedalling is pushing you strongly off the rear of the saddle and you end up compensating by pulling forward with the handlebars. The laid back and upright style is fine for beach path cruising but it sucks for getting to work fast.

Finally there's handlebar positioning. Again if this is a comforty hybrid then you will want to alter it a little to produce a little of a foward lean. If it's a performance hybrid then you should already have the lean. But perhaps it's too much of a lean for you. Not all of us are as in condition or flexible as Lance Armstrong and for those who are not we end up not being as efficient at breathing if we try to bend over too far. If you feel like you can't breath well enough then you may be leaned over too much or you're trying to compensate for too low or far a bar position by crunching your mid section to reach better. That's really bad and you need to alter the bar position so your chest can remain straight and more open so you can breath well. But if it's a comforty hybrid you may be too upright and high. When that happens you end up feeling like you can't push down on the pedals well enough and so you work harder to do less. For this case you WANT to lean forward a little so that you can more efficiently drive the pressure down into the pedals.

For myself I've found that I get my best comfort and efficiency when I'm leaned forward about 20 to 30 degrees in the chest depending on the bike. I play with the saddle and bars to shift the position forward and back until if I just barely lift my butt off the saddle and hands off the grips and try to balance on the pedals I find I'm pretty much balanced and I don't hinge foward or back. This works well for my two mountain bikes that are used for road errands or fast trail riding. Two of my road only bikes are set up to be a little more agressive but still not as aggresive as a full on road crouch. On those I found that for best performance I needed to shift the saddle a hair foward and alter the balance so that I was slightly forward heavy when I tried to balance on the pedals. But certainly if you do this balance test and find that you're back heavy then you'll find you can't get the power to the pedals and it would feel like you're riding uphill all the time.