Not to worry. Getting vaccines delayed by 3-4 weeks is of no great concern. Ideally the vaccines should be given at the times when they are recommended. But due to some reasons or another some do get delayed. These reasons can be minimized but vaccines should be given as soon as possible after the delay. Most vaccines cannot be pre-poned but slight delay is ok.
Get in soon. The recommended schedule is based on giving the vaccines as soon as they can be effective to prevent diseases that could be devastating. Whooping cough is most likely to kill babies under 6 mo of age. You may have been lucky so far but you need to get in and get it done. You would hate yourself if your delay harmed your baby.