on clomid treatment

My doctor started clomid 50mg treatment in jan from 3-7 of my period cause i was diagnosed with PCOS ....she asked me take prometrium from 22nd to 28th day of my period and on 29th day do the pregnency test and i did what she wants me to do...my pregnency test was negitive so i stopped prometrium and i got my period i soon i stopped prometrium ...now i completed my second round of clomid treatment(50mg ) and followed the same process...i did my pregnenecy test on 29th day and it was negitive and i stopped prometrium....it is almost 3 days over but still did not get my periods.....iam worried about this cause i cannot start my 3rd cycle of clomid unless i get my periods....and more over my doctor said that this round also she will give me clomid 50mg only....and next cycle she will increase my dose..(that is 4th cycle)....so for how many days i shoud wait for my periods ...what if i dont get my periods....and my BBT is also very low now....