So does this mean you are just coming back to running after your race in March?
If so, much of this has to do with detraining. Even though the body has run before does not necessarily make it any easier now, however, you may see that you advance much more quickly once you begin your training program.
What makes it difficult for many new runners to understand and that is, our body's cardio-respiratory system responds quite quickly to the stressor of running, but the bones, joints, connective tissue, even muscles can take a SOLID year of consistent running to adapt to the rigors of the sport.
Be patient and allow for a good 48 hour recovery between runs so that your body fully recovers from the stress. And if you live where it is quite warm right now, that may have something to do with your running as well. My pace can easily be a minute per mile slower once the temps hit above 80 degrees.
RUN SPARK STRONG!