Suggest Treatment For Mild Pelvic And Abdominal Pain

Question: I don't know whether I should be worried or whether I'm just being completely paranoid.
I have been experiencing mild pelvic and abdominal pains since around about Christmas time. They are not debilitating or anything like that, they are just something that I am aware of.
Two weeks ago I decided to go to the doctor to check everything was okay. At the time, I was experiencing symptoms of mild pelvic and abdominal pains, with the abdominal pains generally worse during or shortly after eating. I also had some mild lower back ache.
The doctor took a urine sample and said there was a very very small trace of infection, so he gave me trimethoprim for a urine infection (despite me not displaying the typical urine infection symptoms) and said that if my symptoms didn't improve to come back.
The antibiotics made no difference to my symptoms, but I finished the course anyway. During the week in which I took the tablets, I also became aware of my legs becoming uncomfortable when I was relaxed for a period of time (such as when sitting to watch TV or going to bed). The pelvic and abdominal pains persisted.
I went back to the doctor on Friday. He took another urine sample and said that there was no trace of infection, and that he was not convinced I had a urine infection to begin with because the traces of white blood cells were so small.
He examined my abdomen. He said I seemed a bit bloated, but other than that there didn't seem to be anything wrong. He checked for things like hernias as well. He said the pains could be muscular and that he wasn't worried that it was anything serious.
Since Friday I have felt like I also have mild chest pain that comes and goes, and I am suddenly conscious of my bowel movements.
There was a slight trace of blood when I passed stool on Saturday. There wasn't a trace when I passed stool on the Sunday, but it panicked me. I also feel like I am bloated, though I don't really feel bloated, but I think I look bloated.
I made the mistake of looking up my symptoms, and it came up with things like ovarian cancer and bowel cancer, so of course I am now panicking.
I am only 19. I have never smoked, I only drink occasionally, I am fairly active, My only past medical history is coeliac disease, but that is kept well controlled.
In terms of my family history, my gran developed breast cancer in her 50s, but as far as I am aware there are no other cancers in my family. My other gran is riddled with health issues, but she has been for years and none of them seem genetic.
I am just so scared that my symptoms could be something serious! I don't feel unwell, I am just constantly aware of these mild pains now, but I've been to the doctors twice and they don't really seem to have much of an explanation.
In terms of pregnancy possibility, I last had penetrative sex in the middle of November. I have had three periods since. I was slightly concerned as the second of the three periods since this encounter was not normal. It was a light brown discharge, not like my normal flow. However, I put it down to stress and my next period after that was completely normal.
In the middle of December, I came close to sex in that there was genital contact, but no penetration. I got my next period.
The doctor did a urine pregnancy test just for completion when I first went and it came back negative.
In terms of STIs, I have only ever had one sexual partner, and he is the same, so seems very unlikely it could be an STI.
Also I have noticed (I am hyper aware of my body at the moment) that I can feel a pulse in my abdomen. I am currently a medical student and am focusing on cardiovascular at the moment, and I learned the other day that a pulsatile feeling in the abdomen can be a sign of an abdominal aortic aneurysm. I know it is probably silly of me to think I could have that, as I am 19 and don't have a family history of AAAs or any of the risk factors, but again it has panicked me.
Sorry for all the information, I would just really appreciate someone's advice!