Low supply to forceful letdown??

Jen3016

When my LO was 2 weeks old, my pediatrician told me DD was not gaining weight fast enough.  She had only gained 4 oz in one week, and it took her 2.5 weeks to gain her full birth weight back.  So I started fenugreek and pumping to up my supply.  Well now, the last week or so, DD has been fussing at the breast during feedings.  She will eat very aggressively for 5 minutes, then burp, then fuss through the rest of the feeding until we switch sides.  It was a struggle to get her to eat for 10 minutes.  The first 5 minutes she gulps, and sucks fast and hard, and usually has milk dribbled on her cheek/chin and sometimes onto her clothing.   

I asked the LC at my support group today and she said it sounds like forceful letdown and that she's probably gassy.  Can one go from having "low" supply to having over supply?  I'm definitely not going to wish it away, she has been gaining about 8-9 oz per week.  We have had some slightly green poop that the LC said might be because she was having difficulty getting enough hind milk due to not eating more than 10 min per side.  Thanks for any input!