Very abnormal period

When I was 14-17 I was on the deposit shot. It took my period away completely, after I was off the deposit it took a year to get my first period. I'm almost 22 now and my period has lasted 4 months once, and just recently lasted 4 1/2 weeks, off for six days back on for almost 2 weeks and now I'm spotting. I'm overweight, so the doctor is really iffy on giving me BC. I can't stand these long lengths periods anymore! Anyo.e has similar problems?