Your score may go down if you apply too often. Banks make a hard inquiry about your credit, which may affect your score especially if you apply several times in a row. Also, this may result in your credit application being denied due to too many inquires. You should wait about six months before applying for another credit card. That will eliminate the credit score decrease.
Consider credit cards for fair credit. These cards report credit performance to credit bureaus and have low APR. Also they offer a 0% interest introductory period on purchases and rewards.