Have you booked an appointment to speak with a GP? Your symptoms seem to be able to be attributed to a number of possible things. I am not a medical professional but the later in my 30s I have gotten my periods have changed, it’s perfectly possibly perhaps it’s perimenopause symptoms or perhaps are you on birth control that might no longer suit you, however you would likely need bloods drawn to know any of this. I don’t know where your pain is, but abdominal pain comes in so many forms and shapes and sizes and a minute amount will mean something sinister, try not to worry but speak with a GP to put your mind at ease. 
I recently had a mass found in my pelvis and after months of worrying, there is no reason to have been, as it’s a cyst. I know what it’s like to panic but I had to write to you as I feel like I wasted so much time worrying so be your own biggest health advocate and see a doctor, get some answers. Good luck.