I know that feeling, I would advise that you take your ISO up as high as you can before it gets noisy, you can sort that out yourself at home and find where your camera really loses it, (my old D2x was around 800) But the D3100 may well be higher. I have been trying this type of photography for a few years and its tricky and more than difficult to get good results especially at smaller venues, your pics look like they might have been taken in a working mens club or a bigger pub, but the lighting looks a bit poor. The only other advice I can offer you is shoot RAW as you can make more and better adjustments to your images without losing too much detail.
Mind you I do like the pictures although a little dark you have done very well with focus and and framing of the subjects, without being too patronizing, don't give up, you will want to buy faster glass (F1.4 50mm is great) and even think about using flash if you can get away with it, but I have just upgraded to D700 to give me the ISO I need.
Good luck and if you need any other help or tips giver me a shout (providing you like my photos
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