Collection activity hurts your score more when it is recent. Older collection activity does not have as big of an impact on your score. If the collections that you paid were old (let's say 3-4 years old) and you just paid them off - now it looks as if you have recent collection activity because the creditors likely updated your account to show the date of last activity. So, your score goes down. (Bummer, I know)
New credit will almost always hurt you. Another factor in your credit score is the length of your credit history. Within 6-12 months, your score should go back up. Just don't apply for any new credit or you will experience the same thing all over again.
Hope this helps!
Best of luck,