I'm a 17 year old girl experiencing slight discomfort around my mid and lower stomach and I've always had a fairly gassy/rumbling stomach but over the past weeks I've found a few lumps appearing and disappearing, only when I'm lying down. They generally appear in the same spots, one is on the right side of my belly button, one at the lowest part of my abdomen in the middle and one low and slightly to the left.

Today (first day of my period whilst having these lumps, not sure if linked) while standing up I noticed there was a rather large buldge in my lower abdomen which made me worry thinking I could be pregnant but I realised I haven't been sexually active for 2 months and have had a few urine/blood tests since then and even recently. They aren't painful but can be uncomfortable. They don't hurt to push or touch but I am extremely worried, hopefully I'm stressing over nothing. I will be getting a pelvic examination soon and going to the doctors again soon. I've always had intense period cramps and am very thin so this might make them more prominent, I'm unsure? But I have definitely been more stressed lately which may have contributed to it? Also I think my appetite has decreased and I am more bloated. I don't know if this matters but I am on the birth control pill and have noticed some changes (stomach pains after sex, abnormal bleeding but these stopped weeks ago as my body adjusted). 

Any idea what it is, IBS, hernia, something related to my ovaries and uterus or something worse? I'm very worried?