Completing 2 marathons and getting a PB must of taken some training! Well done
Now in my opinion your body just needs more time to recover, because not just have you been training hard but you have had a bug, therefore your body may even need double the time to recover!
Don't worry, Your fitness is still there but to bring it back could take a week or it could take a month depending on how quik your body can recover. So listen to your body it may need more rest or it may want to start getting back into it. The key is Just by starting off very slow and building back your mileage and pace gradually. You need to do light runs and stregnth training and Lay off the big hills to begin with. In my case chrismas and winter always get me, but thats just down to lack of motivation and the wheather sure doesn't help :/
If you want it back, it will come back and way before the VLM