Does this sound like I could be pregnant or my possible menses oncoming?

Hello. I have quite a concern...

My period is always on time and is usually normal. On average, I have one every 33 days. According to a fertility calculator, I was suppose to be fertile between the dates of December 8th to 13th. Well, I had a clear/white discharge on the 9th and had intercourse with my husband that night. (Day 18 from last period) I'm 30 years old and I've really never had this kind of problem.

Right now, I don't have any of the monthly signs except for minor cramping and a mild acne. Yesterday, I tested and it was negative but I'm still really nauseated and have regular mild cramping. Anyway, my period is due on the 25th. (4 days from now) I have had bad nausea with the cramping for the past four days. Today, the cramping has been happening more but it's not bearable. The nausea is all throughout the day. It has been waking me up at night. No puking, just nausea.

About four hours ago, I had gone to the bathroom and had brown discharge. About two hours ago, I went to the bathroom again. I had a severe cramp on the right side. Then when I wiped, I had a little brown and then a reddish/pink discharge. Now I'm just cramping again.

So, I have a few questions. Does it sound like I could be pregnant or my possible menses oncoming? I am beginning to be very restless.