I'm having trouble getting pregnant, but I have all the symptoms of being pregnant?

for a long time now my husband and I have been trying for a baby. I have used ov kits, the recommended positions, propping my bottom up for 20 min or more, and having intercourse every other day ( mind you we keep it very enjoyable not just a routine) the every other day thing seems to keep it fun actually lol. But here is the prob. I was supposed to have my period two weeks ago but it came a little early, I'm a 18 day cycle/ some what irregular, it was just ultra light spotting for 3 days. I have already had 3 little boys but I didn't know I was prego with any of them till around 3 mo. I'm having all the symptoms morning sickness, hungry all the time, hot and cold flashes w/ sweats and w/o, my breasts are very sore, I'm really moody, ect. but this has happened before.. I don't show on urine tests just blood tests... any advise?