physical pregnancy traits

I am not a breeder but have a question. I took in a stray cat that I was convinced was pregnant. The cat got out by mistake and my husband saw her mating. This was in December about the 18th. She was approximately 4-6 months old. I didn't think she had ever gone into heat, or at least not while she's been with me. She's been here since Halloween. I was convinced two weeks ago that she was very pregnant and estimated her due date at first week in Feb. As of two days ago she no longer looks very pregnant. I am trying to determine if she is pregnant. Can you give me some tell-tail signs of pregnancy. I would have swore she was pregnant. I could feel and see her belly just moving, she acted very uncomfortable. Her belly was kind of large. She was not as big as the last pregnant cat I took in but her belly was swelled like she swallowed a grapefruit the other cat looked like she swallowed a cantalope. Her nipple area was swollen slightly, her tets sagging a little. I can't tell if the rest of her has caught up with her belly or if the belly is actually smaller. I know I sound ignorant but this is a financially hard time for me right now and unless its an emergency I would rather not take her to the vet at least not until March. Are there any suretel signs? Any info you can give me would be greatly appreciated.

Other than what you described already the only other way is to have a vet look at her and/or take xrays. Is it possible that she HAD the litter already and you didn't know it?
*EDIT* After checking my gestation matrix, she would be due around the 19 of Feb give or take...
so, either her body is catching up with her, she had a mis-carriage, or she isn't really preggers (false Pregnancy).

I realize that it's a financial strap issue, but.... you really ought to take her to the vet to find the answer, that would be the safest thing to do for her AND you.