How Can Irregular Periods With Longer Mid Cycles Be Treated?

Since the birth of my son nearly 4 years ago now my periods have been very irregular upto 38 days between them. However, in the last year the now range from 40 to 65 days. Is there a logical reason for this and is there a way I can bring them back down to a more normal level as my husband and I have been trying for a second for 3 years now and with no success?