Huge large clots during my period?? Is this normal?

I came on my period 3 days ago today is my 4th day. Usually my periods are heavy but a super+ tampon works and only fills half every 8 hours or so, or that of when needing changing... However last night i had a tampon in for 3 hours went to bed and realised I felt wet below. When I checked i had bled everywhere. I went to the bathroom removed the tampon and wiped myself *not nice to hear i know* but 1 blood clot the size of 2 bouncy balls came out with a gush of blood, followed by another one immediately after. Normally I will expect a tiny amount of clotting when I start my period but this... this shocked me, then 4 hours later when I finally got some sleep, the same occurred again.. I have booked a doctors appointment but they're as much use as a wet lemon.. has anyone else had this problem.. This did occour a few years ago, but they thought it was a heavy flow even after explaining that they normally are they ignored me and gave me tablets to stem the bleeding. I haven't had sex recently.. but have had a water infection.. and have noticed that my periods are becoming more unregulated such as 1 week on 2 week off 1 week on 1 week off 1 week on 2/3 week off... and so on... help??