a long post! OPKs?

Hi ladies. I'm 36 and I'm TTC my 4th. I have a 12 (almost 13) year old from a previous relationship, a 2 year old, and a 1 year old with my husband. All boys!! So, I got the go ahead from my husband to give one last shot to having a girl 😀 I do love my boys with all my heart but I've always wanted a girl so my husband says we can give it a go, though he thinks we'll have another boy. I'm ok with a boy too, just one more try!! Lol 
With that being said, this go around has been a lot different for me. Honestly, my first 2 boys were "accidents" as I got pregnant on birth control with both of them. The first time I had been sick and had been taking several antibiotics over a period of time and wasn't taking it at the same time everyday. I probably missed a day or two and had to catch up if you know what I mean, so I'm thinking that's why I got pregnant then. I was also only 22. I also got pregnant several years later not on birth control but I had a miscarriage super early in the pregnancy. With my second son I was also taking birth control and wasn't trying to get pregnant but my husband and I were pretty busy and I know that I wasn't perfect with the birth control. Moving on to my third. I was breast feeding my 2nd had one period and literally got pregnant the next month without much planning. I was trying to get pregnant again but I had just started thinking about it and bam, I was pregnant. It happened a lot quicker than I expected! I know a lot of you are probably hating me right now because you've been trying so hard for so long and I just seem to get pregnant without a thought! Until now. I've been trying for a good 5 months and haven't been on any birth control since my 3rd was born so you could tack on a couple months of not trying but not preventing. 
Anyway, sorry this is so long!! But I just wanted to get my story out there so you see where I'm coming from. I've been actively tracking my period, CM, and BDing in my fertile window for the last 5 months and my periods have been pretty regular 30 day cycles. I'm obviously not pregnant yet. So, I bought the easy @home OPKs for this month just to see if I can figure out when I'm ovulating to help this along!! I have no clue when to use them though. Do I start as soon as my period is over? I'm on cycle day 3 and sometimes I'm stilling spotting on day 7. And when you get a positive does that mean you ovulate the next day? Any advice on that would be nice 😀 Is this a reliable brand? It also came with 20 hcg tests too! $20 on Amazon!! 
 I know that many of you having been trying for a lot longer and have no children (or have children!!).. I just want to say you ladies are amazing bc I don't know how you do it!!! I'm losing my mind after 5 months! I'm afraid my age is really factoring in to this now and that freaks me out. You're probably wondering why I would start trying to conceive when I had a 6-7 month old BUT I was afraid this age thing was going to play a factor and I really wanted to get going. Now I just keep getting older every month.. I hate being in my late 30's when I still feel like I'm in my 20's and my mind still thinks I am sometimes! Lol 
Would love any advice from you all and to hear your stories as well!!