Perhaps you're not recovering enough between your sprints? Speedwork is hard work, so perhaps sprint to one lampost, then jog for a two-lampost distance, then sprint one, jog two .... etc. etc. Or else just say to yourself pre-run that you're going to do (say) five 100m efforts in your run and drop them in whenever you fancy.
Hope that helps - speedwork is one of those training techniques that shows a result after only a few weeks so keep at it!
Just a thought - if you are going flat out on your sprints ... you don't have to! Just 'faster than normal' is fine for now.