Hi Suzie, do you know that lactic acid only stays in your muscles for up to 2.5 hours after exercise, after that it is absorbed and used by your body. If the tightness you are feeling is the day after the run etc then you should be looking at tight muscles. Maybe increase your stretching before and after your training runs, concentrating on gastrocnemius, soleus and flexor hallucis longus (big toe tendon).
I also agree with the previous posting regarding having a professional sports massage every 2 - 4 weeks.
Hope this helps.
Best regards
Dunantin