It's not clear to me how you could have been on antibiotics, which you say you were, yet you have not seen a doctor. Can you explain? Were you taking old antibiotics you still had in the house? Or a prescription that was for someone else in the house? Doing either is very, very dangerous, if that's what you did. I don't see how it could be otherwise, if you didn't see a doctor.
Please get to the doctor. Why are you scared to go? Because the doctor might find something you don't want to know about? Not every lump is a cancer -- most are not. But if it were anything like that, you would rather leave it undiagnosed and untreated than go see the doctor? You have an infant son. He needs you. Go to the doctor.
It's worrying to me that you put the weight loss question ahead of the question about the lump. The lump gets priority right now, not the weight loss. It's very likely that the lump is or was a cyst or something simple like that, or that the hip issue you feel is something basic, or related to your weight, but we cannot diagnose you over the Internet.
For your son's sake, so he can have a mother who is in good health and not worrying, you need to get medical advice -- in person, and not online.