It's very common. I've had it on and off for years. With Paxil/Paroxetine/Seroxat my erection was about 70-90% too. It was enough to have sex but it didn't feel hard enough to me and wasn't very nice.
I'm now on Escitalopram and erections are more like 90-95% but I take longer to reach orgasm and sometimes there is no pleasure from it. (Which is actually ok because at least now I can have sex and I can 'perform' decently).
With the paxil, changing the dosage helped things, as did eating certain things (I think). I think with both drugs though, half of it is all in your head. The pills do have some effect, but I think it's mostly your frame of mind. If you are a bit anxious and stressed, then you don't get as hard, and you don't get as much pleasure from an orgasm. When you are super relaxed and happy and in a good mood, everything can seem pretty normal. That's how it works for me anyway.
So yeah, try talking to your doctor about changing the dosage. Sometimes increasing the dose can help, strangely. Also, when I complained about weaker erections to my doctor, he said to just take Viagra (even though I was in my mid 20's). He said it's perfectly fine to do that, but I never did that. You might want to try that though.
And if that doesn't work, then what euphoria said is a good idea. From what I've read on the web, there are usually drugs that you can take that counteract the sexual side effects of whatever drug you are taking. My doctor said he didn't want to do that because he said, "It's simply bad medicine to prescribe a second drug to ease the effects of the first drug", so he preferred to just put me on a different medicine to begin with. But a more open minded doctor might give it a shot.
Currently taking 20mg of Paroxetine (Seroxat). It's not very useful. Better than nothing.. but only just.