What is happening to me

Hello, I am 35 years and have been having weird symptoms for a couple of months now. I had sex using the pull out method a couple of times and two months ago I noticed I had a shorter period regular for about two days and brown stains the following three days. I normally have moderate flow for about three days before it reduces. This happened last month as well... my next period is due in three days now.

I have been experiencing fullness in my stomach, rough facial skin, bitter mouth,slight bust increase and a bit of weight gain. I would love to have a child someday but I am not ready just yet . I have had three blood tests and one scan done so far and they all came out negative. 

I have been reading a bunch of stuff off the internet which is just confusing me further.I am very stressed about this and finding it difficult to sleep because I do not know what is happening to me.

I will really appreciate it if someone could shed some light. Thanks.