Sorry to hear about your slump.  I was in a very similar situation a while back, and it took me a month or two to figure it all out.  It sounds like after the first game, the part of the lane you're playing is drying up.  The ball will either pick up too early if you throw it slower, or won't pick up at all if you throw it harder.

What I would suggest is once the oil starts to change, move quite a bit left or right to get into a new part of the lane.  I would say move right (this is all assuming you're a righty) at first, and move a good 5 boards right to get away from the area you were originally playing.  Try that part of the lane, and if it isn't working well, then move left of where you were originally.  And if neither of those moves produce results, then it may be a mismatch of gear and you might need to look at weaker equipment, or polishing your ball up now.

To practice adjusting to lanes, what I did/do is go to open bowling after a night where there's only ONE league and then open bowling.  This way you have lanes that have only a handful of games on it, enough to change the lanes from how they started, and you can really work on how to bowl during lanes that are in transition.

Good luck, and I hope everything works out well!
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Proud Supporter of Rob Stone
Obviously, you aren't a golfer.
Some stayed in the foothills, some washed logs like teeth.

I usually slump pretty badly about once a season.  Yes you can work yourself out of them.  However, I would strongly recommend seeing a good coach.  They have trained eyes and can spot stuff that you probably don't even know you're doing.  I went through this earlier this year.  Mine lasted about 2 months with no end in sight.  I went to a guy that I know is top notch and that I trust.  The changes were simple and I went right back to scoring the way I knew I could.  Your frustration will only lead to worse results that may eventually turn around, but why go through that?

Don
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"You cannot change the stripes of a leopard."
~Emmitt Smith

slumps are hard to get out of sometimes. like someone said earlier, gt back to basics. one thing that helps me is going back to a practice drill i used to do. i would bowl a game starting at first arrow, stay there till i get a pocket strike then move to the next arrow and repeat. bowl a whole game like this. all the while im tinkering things like my release and grip pressures to get the ball to strike. a couple of games of this really helps, and it teaches you to be versatile. once you can change releases and grips and grip pressures, you'll be a better bowler and the slumps wont last as long. another person suggest that the center cut back on lane oil and they are right, most centers shorten the length and some cut back on volumes of the pattern cause less people bowl in the summer. before you go buy a new ball, simply change the surface first with your proshop guy. theres no need to buy a new ball just for s summer league. without knowing the lane surface of the center you bowl in, or your style i really cant tell you how high to go on surface but ill bet you you need to go up, and maybe some polish.
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STORM:If You Hear The Thunder,Sorry,The Lightning's Already Struck!