As you may be aware, taking Testosterone shots will cause your body to reduce your LH production to almost zero.
LH is a hormone, its purpose is to signal your testicles to produce Testosterone.
So during a cycle you will not be producing none of that.
Depending on how much ylou take and for how long, the testicles may noticeably shrink as due to their low activity, blooddlow will be reduced.
Due to this "dormant" state, damage may occur, and after the cycle ends and your body starts to produce LH again, test production may increase only very slowly and may take months to even feel alright, and in some cases it may never go back to what it was before the cycle.
This period of low testosterone condition, apart from causing a plethora of terrible symptoms, will probably have you loose more than you gained during the cycle.
Your body will convert some Testosterone into Estrogen, so if you increase tesy you are increasing Estrogen as well, which is fine until you have way more test than Estrogen, as it is the ratio that is the most important aspect.
After your last injection, your Testosterone levels will gradually fall, but as Estrogen is expelled at a slower rate, the ratio will shift towards having more estrogen than Testosterone, which causes feminisation symptoms like growth of breast tissue, muscle loss, increase in fat storage in areas like glutes and outer things etc.
This messed up hormonal ratio will also signal your body to produce less Testosterone, making recovery even slower.
There are ofcourse methods to avoid all this, basically you will need to take some supplements while on cycle (in particular Taurine seems to protect testicles from damage caused by steroids), and procure an Aromatase Inhibitor medication that will greatly reduce how much of your Testosterone is converted into Estrogen (you need to have some estrogen, so it's important not to dose the AI too high).
Ofcourse blood tests are needed to see what the hormone levels are and if and how much AI to take.
Some people choose to do a thing called PCT (post cycle therapy) after the cycle ends, and that usually means to take a combination of two SERMs, Clomiphene Citrate (Clomid), and Tamoxifen Citrate (Nolvadex), that will have the effect of gretly increasing (temporarily) your LH production and block the effects of Estrogen on your breasts.
Now, if you did things right during the cycle PCT might not be necessary, but I would prefer some of the more experienced members give you a protocol.
Normally the suggested AI is Exemestane (Aromasin), as it has the effect profile that is the most suited to regulate Estrogen production while taking steroids.