Should I see a doctor?

Right well me and my partner have been ttc for two years now to no avail however I do have irregular periods so I am just putting it down to that. On Jan 6th we dtd and then on the 17/18th I bled so unbelievably lightly I was certain it wasn't my period. anyway last Saturday I did a test and it was a bfn. out of curiosity I did a opk and it came up that I was having my surge so we bd'ed sat-tues I know if I have conceived it wouldn't show yet but why on earth did I randomly bleed like that as when I do actually have af it's always really heavy and 4+days.... may I also add I have been having strange symptoms i.e loss of appetite, ache in my lower abdomen, achey boobs etc. It just doesn't make sense specially when I put it all alongside my bbt chart and cm log